bluuebunny/crossref_metadata_2025_split huggingface dataset:
Locating sensors in complex chemical plants based on fault diagnostic observability criteria
Authors: Raghuraj Rao , Bhushan Mani , Rengaswamy Raghunathan 
Published: April 2004

AbstractFault diagnosis is an important task for the safe and optimal operation of chemical processes. Hence, this area has attracted considerable attention from researchers in the past few years. A variety of approaches have been proposed for solving this problem. All approaches for fault detection and diagnosis in some sense involve the comparison of the observed behavior of the process to a reference model. The process behavior is inferred using sensors measuring the important variables in the process. Hence, the efficiency of the diagnostic approach depends critically on the location of sensors monitoring the process variables. The emphasis of most of the work on fault diagnosis has been more on procedures to perform diagnosis given a set of sensors and less on the actual location of sensors for efficient identification of faults. A digraph‐based approach is proposed for the problem of sensor location for identification of faults. Various graph algorithms that use the developed digraph in deciding the location of sensors based on the concepts of observability and resolution are discussed. Simple examples are provided to explain the algorithms, and a complex FCCU case study is also discussed to underscore the utility of the algorithm for large flow sheets. The significance and scope of the proposed algorithms are highlighted.
Solvent recovery targeting
Authors: Ahmad Berit S. , Barton Paul I. 
Published: April 2004

AbstractOne of the environmental challenges faced by the pharmaceutical and specialty chemical industries is the widespread use of organic solvents. With a solvent‐based chemistry, the solvent necessarily has to be separated from the product. Chemical species in waste‐solvent streams typically form multicomponent azeotropic mixtures, and this often complicates separation and, hence, recovery of solvents. A design approach is presented whereby process modifications proposed by the engineer to reduce the formation of waste‐solvent streams can be evaluated systematically. This approach, called solvent recovery targeting, exploits a recently developed algorithm for elucidating the separation alternatives achievable when applying batch distillation to homogeneous multicomponent mixtures. The approach places the composition of the waste‐solvent mixture correctly in the relevant residue curve map and computes the maximum amount of pure material that can be recovered via batch distillation. Solvent recovery targeting is applied to two case studies derived from real industrial processes.
Thermocapillary pumping of discrete drops in microfabricated analysis devices
Authors: Sammarco Timothy S. , Burns Mark A. 
Published: April 2004

AbstractA nonmechanical pumping mechanism, thermocapillary pumping (TCP), is described for moving nanoliter‐ and picoliter‐sized drops of liquid within microfabricated flow channels. In TCP, one end of a single drop is heated to create a surface tension difference between the ends of the drop. The induced surface tension difference causes a capillary pressure difference between the two drop ends and results in drop motion. TCP velocities of up to 20 mm/min were measured for several liquids at temperature differences between 10 and 70°C. An expression developed for TCP velocity yields predictions that agree with experimental velocities within corresponding uncertainty limits. Several techniques for assisting TCP are also suggested when contact angle hysteresis, the major factor limiting TCP velocities, is too large. These techniques include using surface treatments to reduce the contact angle hysteresis, converging channels to offset hysteresis, or an applied pressure to assist in movement.
Combined calcination, sintering and sulfation model for CaCo3‐SO2 reaction
Authors: Mahuli Suhas K. , Agnihotr Rajeev , Jadhav Raja , Chauk Shriniwas , Fan L.‐S. 
Published: April 2004

AbstractA mathematical model developed accounts for the multiple rate processes involved in the reaction of solid CaCO3 or Ca(OH)2 with SO2 at high temperatures in the combustion environment. The model, based on the grain‐subgrain concept, considers the concomitantly occurring calcination, sintering and sulfation reactions and their interactive effects on pore structure and reaction kinetics. It incorporates internal diffusion, reaction, and product layer diffusion in simulating the calcination of the CaCO3 grain and subsequent sintering and sulfation occurring on the CaO subgrains. It is the first sulfation model to incorporate the true mechanism of diffusion through the solid product phase: the solid‐state ionic diffusion of Ca2+ and O2− ions in a coupled manner through the nonporous CaSO4 (Hsia et al., 1993, 1995). Its predictions are compared with the random pore model (Bhatia and Perlmutter, 1981a) and the grain model (Szekely and Evans, 1971) using experimental CaO sulfation data from the literature as well as short‐contact‐time CaCO3 and Ca(OH)2 sulfation data reported previously. Mahuli et al. (1997) discussed a high reactivity modified calcium carbonate synthesized by optimizing the pore structural properties. This modified CaCO3 can convert 70–75% of sulfation within 0.5 s, which is substantially higher than any other sorbents reported for similar particle size and reaction conditions. The model is used to predict the calcination and sulfation kinetics, as well as to simulate the surface area evolution of the modified CaCO3, which provides further insights into its exceptional reactivity.
Theoretical analysis on extrusion die flow of electronic packaging materials
Authors: Pan Jing‐Pin , Liu Ta‐Jo , Wu Ping‐Yao 
Published: April 2004

AbstractA mathematical model has been developed to describe the extrusion die flow of reactive electronic packaging materials. This model assumes that the flow is 1‐D in the manifold of the die, but the flow obeys the 2‐D Hele–Shaw model in the slot section. A realistic viscosity expression that includes the effects of chemical reaction and heat transfer has been adopted. A linearly tapered coat‐hanger die was selected for illustration and the packaging material was chosen to be the epoxy system. Some example calculations are presented to illustrate the effects of several parameters on the flow distribution. Two optimization approaches were adopted to improve the uniformity of the flow; both the Taguchi method and the method of inserting a specially designed choker bar are applicable. However, using a choker bar appears to be more effective and flexible.
NMR imaging of flow velocity in porous media
Authors: Chang C. T. Philip , Watson A. Ted 
Published: April 2004

AbstractTwo NMR velocity imaging methods based on the pulsed field gradient stimulated‐echo technique are evaluated for the measurement of fluid flow in porous media. The spatial resolution and dynamic scale of velocity imaging experiments are chosen to represent the macroscopic behavior of the complex motion of fluid molecules. A theoretical formulation for data interpretation is presented and demonstrated with experimental data for water flow in a glass‐bead pack and sandstone samples. Velocity imaging methods investigated include the use of flow‐induced phase shifts and the measurement of spatially resolved velocity distributions. The results show that the phase‐shift method is not suitable for some porous media. By contrast, the measurement of spatially resolved velocity distributions not only allows a map of mean velocity to be determined, but also provides information about the velocity field within each elemental volume of the image.
Prediction of flow fields in a dual‐impeller stirred vessel
Authors: Micale Giorgio , Brucato Alberto , Grisafi Franco , Ciofalo Michele 
Published: April 2004

AbstractNumerical simulations were conducted for the flow field in a baffled tank stirred by a dual Rushton impeller. For this geometry, LDV measurements show a characteristic dependence of the flow patterns upon the position of the impellers. Two advanced modeling approaches were tested. In the first, the vessel was divided into two concentric blocks, coupled by a sliding grid technique, and simulations were conducted in time‐dependent mode. In the second approach, the vessel was modeled as two partially overlapping regions, the inner one rotating with the impeller and the outer one stationary; simulations were run in steady‐state mode for each of the two regions, while information was iteratively exchanged between them after azimuthally averaging and transforming for the relative motion. A third set of simulations was conducted for comparison purposes by using a more conventional method, in which the impellers were not explicitly simulated, while their effects were modeled by imposing suitable values of velocities and turbulence quantities (derived from single‐impeller experiments) at the blade periphery. The first two techniques gave similar predictions and successfully reproduced the dependence of the flow patterns on the position of the impellers. The latter method required far less computational effort. On the other hand, the impeller boundary conditions technique failed to reproduce the experimental flow patterns, because of the inadequacy of single‐impeller boundary conditions for the present geometry.
New thermally coupled schemes for ternary distillation
Authors: Agrawal Rakesh , Fidkowski Zbigniew T. 
Published: April 2004

AbstractThe fully thermally coupled system of distillation columns for ternary separation has two, two‐way connections between the columns. New, simplified (and easier to control) systems of columns for ternary separations, with a reduced number of connecting streams, are proposed. The new systems contain one one‐way and one two‐way connection between the columns. Depending on which connection is located on top and which phase stream (liquid or vapor) is used in the one‐way connection, there are four possible configurations for these new systems. For certain feed compositions and relative volatilities of components, these new systems can replace the fully thermally coupled system of columns without any increase in energy demand. The optimum system selected from the four proposed configurations consumes no more, and frequently much less, energy than the side stripper or side rectifier configurations or than a system with a prefractionator.
Modeling permeation of binary mixtures through zeolite membranes
Authors: van de Graaf Jolinde M. , Kapteijn Freek , Moulijn Jacob A. 
Published: April 2004

AbstractThe separation of ethane/methane and propane/methane mixtures with a silicalite‐1 membrane was investigated as a function of composition, total hydrocarbon pressure (up to 425 kPa), and temperature (273–373 K). The selectivity of the membrane is highly dependent on these operating conditions. The generalized Maxwell–Stefan equations were used to predict the fluxes and the associated selectivities. These model predictions, based on separately determined single‐component adsorption and diffusion parameters, were in excellent agreement with the experimental data. Using the empirical Vignes relation for the prediction of the binary Maxwell–Stefan surface diffusivity, there were no fitting parameters involved in the model prediction. The importance of incorporation of adsorbate–adsorbate interactions in the model is clearly shown, both for transient and steady‐state mixture permeation. Theoretical analysis showed that for mixtures of a fast, weakly adsorbing component and a slow, strongly adsorbing component the maximum selectivity obtained with microporous membrane separation is always a factor of 2 lower than the one obtained under equilibrium adsorption conditions.
Pervaporation for the mixture of benzene and cyclohexane through ppop membranes
Authors: Sun Yi‐Ming , Chen Yuan‐Kai , Wu Chi‐Huang , Lin Albert 
Published: April 2004

AbstractPervaporation and sorption for the liquid mixture of benzene and cyclohexane by using poly[bis(phenoxy)phosphazene] (PPOP) membranes were characterized. Diffusivities, solubilities, interaction parameters, plasticization coefficients, and heats of sorption for benzene and cyclohexane in the membrane were determined from the vapor sorption kinetics and isotherms, which were measured gravimetrically by a continuous microbalance. Pervaporation operations offered a maximum selectivity of 3 at 35°C and the 35–50% feed concentration level of benzene. Normalized fluxes increased but the pervaporation selectivity decreased slightly with temperature. The binary transport in the membrane was modeled by the solution–diffusion model with an exponential form diffusivity to the concentration of each permeant. Coupling coefficients imbedded in the model were numerically determined by a proposed computation method. The model can illustrate not only concentration and diffusivity profiles for the permeants within the membrane, but their transport mechanism, which is consistent with the hypothesis of “two layers” in the membrane. The analysis of activation energy for transport indicates that the permeation barrier for pervaporation is reduced much more than that of the single‐vapor permeation through an unswollen membrane.
Effects of carbon‐to‐zeolite ratio on layered bed H2 PSA for coke oven gas
Authors: Lee Chang‐Ha , Yang Jaeyoung , Ahn Hyungwoong 
Published: April 2004

AbstractEffects of carbon‐to‐zeolite ratio on a layered bed H2 PSA using activated carbon and zeolite 5A were studied experimentally and theoretically. Coke oven gas (56.4 vol. % H2, 26.6 vol. % CH4, 8.4 vol. % CO, 5.5 vol. % N2, and 3.1 vol. % CO2) was used as a feed gas for the seven‐step two‐bed PSA process incorporating a backfill step. In these experiments, the effects of three operating variables such as adsorption pressure, feed rate and purge rate on the performance of a layered bed PSA were investigated. The layered bed gave better purity than the single‐adsorbent bed at the same operating condition, except at low purge rate. Since every component had its own front velocity at each layer, a carbon‐to‐zeolite ratio affected product purity at a given recovery or throughput. Moreover, for a high‐purity H2 product from coke oven gas, an optimum carbon‐to‐zeolite ratio had to be determined to control a leading wavefront of N2. In layered bed PSA processes, the temperature variations inside the bed reflected a kind of inflection or plateau at which a roll‐up phenomenon occurred and showed the dynamics of adsorption well at each step during a cycle. Simulated results of the dynamic model incorporating mass, energy and momentum balances agreed well with the PSA experimental results.
Hybrid first‐principles/neural networks model for column flotation
Authors: Gupta Sanjay , Liu Pi‐Hsin , Svoronos Spyros A. , Sharma Rajesh , Abdel‐Khalek N. A. , Cheng Yahui , El‐Shall Hassan 
Published: April 2004

AbstractA new model for phosphate column flotation is presented which for the first time relates the effects of operating variables such as frother concentration on column performance. This is a hybrid model that combines a first‐principles model with artificial neural networks. The first‐principles model is obtained from material balances on both phosphate particles and gangue (undesired material containing mostly silica). First‐order rates of net attachment are assumed for both. Artificial neural networks relate the attachment rate constants to the operating variables. Experiments were conducted in a 6‐in.‐dia. (152‐mm‐dia.) laboratory column to provide data for neural network training and model validation. The model successfully predicts the effects of frother concentration, particle size, air flow rate and bubble diameter on grade and recovery.
Dynamic behavior of iron forms in rapid reduction of carbon‐coated iron ore
Authors: Sugawara Katsuyasu , Morimoto Koji , Sugawara Takuo , Dranoff Joshua S. 
Published: April 2004

AbstractAs a part of a fundamental study of the kinetics of rapid smelting reduction of iron oxide with solid carbon, particles of carbon‐coated iron ore were prepared by heating a mixture of iron ore and phenolphthalein (a model compound of coal tar) at 773 K in a nitrogen stream. The reduction behavior of the carbon‐coated iron ore particles during rapid heating was studied using a drop‐tube reactor at temperatures from 1,073 to 1,773 K. The reduction extent increased rapidly with the beginning of melting at temperatures over 1,650 K, reaching 60% at 1,773 within 0.7 s. The observed changes in the distribution of iron states in the particles were successfully simulated.
Carbochlorination of tantalum and niobium oxides: Thermodynamic simulation and kinetic modeling
Authors: Yang Fenglin , Hlavacek Vladimir 
Published: April 2004

AbstractCarbochlorination reactions of tantalum and niobium pentoxides represent an interesting route of extraction of tantalum and niobium from ores or minerals. Both reactions have not been systematically studied in the literature. The kinetic study reported here was carried out in a fixed‐bed reactor in a temperature domain T = 800–1,000°C. The products of the reaction under the conditions studied are in the gaseous phase. With CO as a reducing agent, the reactions in question are of the noncatalytic gas–solid type, and the experimental data fit the shrinking core model. When using carbon as a reducing agent, the reactions are of the gas–solid–solid type, and the reactivity is much higher than that using CO alone. A reaction model based on phase boundary control was used to process the experimental data. Thermodynamic calculations revealed that at temperatures below 1,000°C the carbochlorination reactions result in the corresponding pentachlorides.
Methane hydrate crystallization mechanism from in‐situ particle sizing
Authors: Herri J. M. , Pic J. S. , Gruy F. , Cournil M. 
Published: April 2004

AbstractA new experimental setup that makes possible in‐situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.
Dynamic behavior issues in three‐way catalyst modeling
Authors: Koltsakis Grigorios C. , Stamatelos Anastasios M. 
Published: April 2004

AbstractMathematical modeling of three‐way catalytic converter (3WCC) operation is used increasingly in automotive catalyst and converter systems optimization. The majority of these models employ a “quasi‐steady” approach in the reaction kinetics computations, which is useful in predicting real‐world performance of the catalyst. However, certain improvements produced by the application of specially tuned redox oscillations cannot be predicted. The approach presented embodies certain types of dynamic phenomena in an existing 3‐WCC quasi‐steady model. The dynamic model based on this approach is validated against data in the literature and experimental results. It is confirmed that the catalyst behavior under dynamic exhaust composition conditions significantly differs from predictions under the quasi‐steady‐state assumption. Oxygen storage and the transient character of water gas shift reaction affect dynamic behavior. The results of this investigation encourage further application of mathematical modeling in such areas as lambda control strategy optimization that lie beyond the scope of traditional 3WCC models.
Estimation of pure compound properties using group‐interaction contributions
Authors: Marrero‐Morejón Jorge , Pardillo‐Fontdevila Eladio 
Published: April 2004

AbstractA family of models proposed here estimate the critical constants and normal boiling points of pure organic compounds from chemical structure by using a new structural approach called group‐interaction contributions, which considers the contributions of interactions between bonding groups in the molecule instead of the contributions of simple groups. Compared to the conventional group‐contribution techniques, the proposed models demonstrate significant improvements in accuracy, as well as the ability to distinguish among isomers.
RTD analysis of a novel Taylor‐Couette flow device for blood detoxification
Authors: Ameer G. A. , Grovender E. A. , Obradovic B. , Cooney C. L. , Langer R. 
Published: April 2004

AbstractHeparin is an anticoagulant used in extracorporeal procedures such as hemodialysis and open heart surgery. Unfortunately, heparin may induce potentially fatal complications in patients at high risk of bleeding. The use of an immobilized heparinase I reactor makes heparin therapy safer, but the design of a safe and efficient reactor for medical use had been a significant problem. A novel reactor, based on simultaneous separation‐ reaction and Taylor‐Couette flow, was designed and successfully tested in vitro with human blood and ex vivo in sheep. The objective of this study was to understand the flow dynamics in the reactor in order to predict and optimize heparin neutralization. Residence‐time distribution studies were performed and a mathematical model was developed. The model was able to predict experimental conversions within a mean relative error of 5.5%. Bypass flow through the reactive section was also predicted.
Maximum stable bubble size and gas holdup in high‐pressure slurry bubble columns
Authors: Luo Xukun , Lee D. J. , Lau Raymond , Yang Guoqiang , Fan Liang‐Shih 
Published: April 2004

AbstractExperiments of pressure effects on gas holdup and bubble size in slurry bubble columns at 5.6 MPa and at gas velocities up to 45 cm/s indicate that the gas holdup increases with an increase in pressure, especially at high slurry concentration. At ambient pressure, a higher solids concentration significantly lowers gas holdup over the entire gas‐velocity range, while at 5.6 MPa, the effect of solids concentration on gas holdup is relatively small at gas velocities above 25 cm/s. An empirical correlation was developed based on these data and those in the literature to predict gas holdup in bubble and slurry bubble columns over a wide range of operating conditions. An analysis of bubble flow characteristics during dynamic gas disengagement indicates that large bubbles play a key role in determining gas holdup due to the large bubble and wake volumes that induce the acceleration of small bubbles. Direct measurement of bubble size shows that elevated pressures lead to smaller bubble size and narrower bubble‐size distributions. Bubble size increases significantly with increasing solids concentration at ambient pressure, while at high pressures this effect is less pronounced. A theoretical analysis of circulation of gas inside the bubble yields an analytical expression for maximum stable bubble size in high‐pressure slurry bubble columns. Based on this internal circulation model, the maximum stable bubble size at high pressures is significantly smaller due to the high gas inertia and low gas–liquid surface tension. The smaller bubble size and its reduced bubble rise velocity account for the observed pressure effect on gas holdup.