bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast numerical simulation for full bore rupture of pressurized pipelines
Authors: Mahgerefteh Haroun , Saha Pratik , Economou Ioannis G. 
Published: April 2004

AbstractAn efficient numerical simulation (CNGS‐MOC), based on the method of characteristics for simulating full bore rupture of long pipelines containing two‐phase hydrocarbons, was developed. The use of curved characteristics, in conjunction with a compound nested grid system, as well as a fast mathematical algorithm, lead to a significant reduction of CPU time, while improving accuracy. The model is validated extensively against field data including those obtained during the Piper Alpha tragedy, as well as the Isle of Grain depressurization tests. Its predictions are compared with those based on other mathematical models including PLAC, META‐HEM, MSM‐CS, as well as BLOWDOWN. Both CNGS‐MOC and META‐HEM produce reasonably accurate predictions with the remaining models assessed performing relatively poorly.
Effects and control of humidity and particle mixing in fluid‐bed granulation
Authors: Schaafsma Stefan H. , Kossen Nico W. F. , Mos Marinus T. , Blauw Levy , Hoffmann Alex C. 
Published: April 2004

AbstractThe novel technique of spraying binder liquid in pulses of short duration on a bubbling fluidized bed was used to study the effect liquid distribution, mixing, and relative humidity has on granule growth. Two important mixing zones in the fluid‐bed granulation process are identified. First, the wetting zone, where the spraying rate relative to the surface renewal rate determines the wetting of the granules and powder. The surface renewal has to be sufficient to prevent overwetting of the surface, which would result in defluidization of the bed. Second, the bulk zone, where the turnover rate of granules relative to the drying rate may determine the secondary growth rate of granules. The granule growth is influenced by the adsorption of moisture on the fluidized particles governed by the relative humidity of the interstitial gas, due to enhancement of interparticle forces and reduces the mixing intensity. Spraying with pulses has a great potential for controlling the granulation process.
Molecular‐weight distribution attainable in a batch free‐radical polymerization
Authors: Yoo Kee‐Youn , Rhee Hyun‐Ku 
Published: April 2004

AbstractThe attainable values of molecular‐weight distribution (MWD) specified by the degree of polymerization and the polydispersity in a batch free‐radical polymerization reactor are described. The two‐step method based on the quadratic profile of the instantaneous degree of polymerization is used to obtain the recipe producing the polymer with the desired MWD specification. The analytic solution for the quadratic profile is derived and analyzed in order to estimate the attainable MWD given the constraints on the range of the instantaneous degree of polymerization. The entire computational procedure is intelligently organized, and thus the actual computational load is very low compared to the conventional optimization scheme. The MWD attainable under a specific operating condition with constraints in a batch styrene polymerization reactor is visualized and various reactor temperature trajectories that would produce the desired polymer product are calculated. The ability to predict the attainable MWD allows an engineer to easily design the recipes that would meet the desired MWD specification.
Optimal design of a subsurface redox barrier
Authors: Chilakapati Ashok 
Published: April 2004

AbstractHarmful contaminants such as chromium (Cr+6), and TCE can be removed from groundwater by reactions with reduced subsurface sediments. Establishing an in situ Fe(II) barrier through the reduction of soil‐bound Fe(III) to Fe(II) by injecting a sodium dithionite (Na2S2O4) solution is studied. Critical to this problem is the possible formation and expansion of a zone around the injection, where all the soil‐bound Fe(III) is reduced to Fe(II). Different reaction models apply inside and outside of this zone so that a determination of this moving boundary is a fundamental part of the solution. The complete analytic solution to this problem was used to develop optimal process parameters, such as injection rate and operational time, that maximize the radius of the Fe(III)‐reduced zone when a given mass of sodium dithionite is injected at a well. When a large reduction [>63% of initially present Fe(III)] is desired, the results indicate that it is better to use a low flow rate to form a Fe(III)‐free zone around the injection. The opposite is true for smaller reductions (<63%), so that a faster injection rate that avoids the formation of the Fe(III)‐free zone yields a larger reduction zone.
Dynamics of two‐phase flow in porous media: Simultaneous invasion of two fluids
Authors: Hashemi Mehrdad , Dabir Bahram , Sahimi Muhammad 
Published: April 2004

AbstractModels of two‐phase flow and displacement in porous media developed so far typically involve one displacing (invader) and one displaced (defender) fluid. However, in many important applications of these phenomena at field scales, such as two‐phase flow in fractured porous media, as well as in laboratory studies, require at least two invaders which also act as the defenders. The results of extensive Monte Carlo simulations of a novel model of such phenomena are reported. The porous medium is represented as a network of pore throats and pore bodies to which effective sizes are assigned that are selected from a given distribution. Both 2‐D and 3‐D networks are used. The simulation results indicate that the structure of the fluids' clusters is volatile, that is, it changes with the time t and length scale. Moreover, ns (s, t), the number of fluid clusters of size s, 〈s(t)〉, the mean cluster size, and S(t), the saturation of the fluids all vary with t in a manner that resembles an oscillatory behavior. This behavior is caused by the dynamic breakup and recoalescence of the fluids' clusters, which is a result of simultaneous invasion of the two fluids. The flow effect of thin wetting fluid films on the dynamics of the displacement is strong over a broad range of the capillary number. Novel dynamical scaling laws for the cluster‐size distribution are obtained. Some results agree qualitatively with the experimental observations, while others provide rational explanations for some unexplained data.
Effect of fluid motion on the aggregation of small particles subject to interaction forces
Authors: Melis Stefano , Verduyn Marcel , Storti Giuseppe , Morbidelli Massimo , Bałdyga Jerzy 
Published: April 2004

AbstractThe effect of bulk fluid motion on aggregation of small particles subject to interaction forces of the DVLO type is investigated. In particular, the convection‐diffusion equation for the probability of finding two particles at a given relative position is solved numerically for the case of an axisymmetrical linear flow field, which approximates a turbulent flow field. The effect of bulk motion is shown to be important particularly in the case of thick double layers, where a critical size exists above which aggregation exhibits a self‐accelerating behavior, that is, the aggregation rate constant increases with particle size. On the other hand, systems with thin double layers appear to be almost unaffected by shear. An approximate criterion for distinguishing between these two cases is presented.
Necessary condition for pulsing flow inception in a trickle bed
Authors: Cheng Zhen‐Min , Yuan Wei‐Kang 
Published: April 2004

AbstractBased on the three existing forms of liquid in a trickle bed, as proposed by Charpentier et al. (1968a,b), a straight channel model is developed with a wall constituted from the packing. Within the channel, liquid and gas phases are assumed to flow concurrently downward at constant velocities, just as in an empty pipe. Since the channel wall is assumed to be formed from the packing, the capillary influence could be taken into account. Capillary and frictional forces are considered as the two principal factors which determine the stability of the liquid film covering a pellet. Evaluating the balance of these two factors gives rise to a new model, which is considered the necessary condition for pulsing flow inception corresponding to the original work by Ng (1986).
Particle mixing in rotating fluidized beds: Inferences about the fluidized state
Authors: Qian Gui‐Hua , B´gyi Istv´n , Pfeffer Robert , Shaw Henry , Stevens John G. 
Published: April 2004

AbstractParticle motion in a rotating fluidized bed was studied by observing the mixing of two layers of particles of different colors. The particles in the two layers were either nearly identical, except for their color, or were of different density and size distribution. All of the particles were in the Geldart‐A classification for conventional fluidized beds. After fluidization, but before mixing, the bed exhibited some fluid‐like behavior, that is, the inner surface became radially uniform. For particle layers of the same material, mixing occurred after Umfc was reached, with bubbles observed at the mixing velocity. No experimental difference between Umb and Umfc could be discerned; they either coincided or were nearly equal. Bubbles appeared to be responsible for particle motion and mixing. When the denser particles are placed on the distributor, the mixing behavior was similar to that observed for layers of the same material. However, when the less dense particles are placed on the distributor, mixing is dominated by differences in density and occurs before bubbles are visible.
Simulated moving‐bed units with extra‐column dead volume
Authors: Migliorini Cristiano , Mazzotti Marco , Morbidelli Massimo 
Published: April 2004

AbstractSimulated moving‐bed (SMB) technology is attracting increased interest for application to the separation of pharmaceuticals and fine chemicals, particularly to enantioseparations. Unlike the large‐scale UOP Sorbex process, these small‐scale units use a series of HPLC columns, and the volume of the connecting lines may become comparable to the volume of the columns. In this work the effect of extra‐column dead volume on SMB performance is analyzed, with the aim of providing a conceptual framework to account for it. In particular, guidelines to design SMB operating conditions with nonnegligible extra‐column dead volumes to achieve the desired separation performance are provided. These are quantitatively assessed through comparison with the results obtained using a detailed SMB model, which accounts for extra‐column dead volumes. The model allows the extent and the role of extra‐column band broadening due to the presence of dead volumes to be evaluated. A set of experimental results on a laboratory SMB unit is discussed in light of the theoretical findings.
Nonisothermal model for gas separation hollow‐fiber membranes
Authors: Coker D. T. , Allen T. , Freeman B. D. , Fleming G. K. 
Published: April 2004

AbstractA model for multicomponent gas separation using hollow‐fiber membrane modules is presented that explicitly accounts for heating or cooling inside membrane permeators due to gas expansion. The model permits simulation of countercurrent contacting with permeate purging (or sweep). The numerical approach permits rapid and stable solutions for cases with many components, even when the mixture contains components with widely varying permeability coefficients. Simulation results are presented for natural‐gas sweetening, a commercially significant application, using polymer permeation properties similar to those of a high‐performance polyimide. For some conditions, temperature decreases from the feed to residue end of the module by as much as 40°C. As CO2 concentration in the feed increases or as stage cut increases, the temperature decrease from feed to residue increases. Relative to an isothermal case, expansion‐driven cooling reduces stage cut at a given feed flow rate since gas permeability decreases with decreasing temperature. Neglect of expansion‐driven cooling in natural‐gas separation simulations can lead to large errors in estimating the amount of feed gas that can be treated to achieve a fixed residue composition. For 30% CO2 feed concentration, if the effective membrane thickness is halved, only a 20% increase (rather than almost a factor of 2) in the amount of gas that can be treated per unit area is obtained due to the impact of expansion‐driven cooling on gas flux.
Optimal design of crystallization‐based separation schemes
Authors: Cisternas Luis A. 
Published: April 2004

AbstractA network flow model is presented for synthesizing crystallization‐based separations for multicomponent systems. The construction of the network flow is based on the identification of feasible thermodynamic states. The method allows consideration of several operation temperatures, complex solid–liquid equilibrium behavior, and several multicomponent feeds and products. For systems with two solutes a linear programming model is obtained, while for systems with three or more solutes a nonlinear programming model is obtained. The relative composition diagram is proposed to determine feasible operation points. For a small problem the relative composition diagram can be used to recognize flowsheet alternatives. For large problems, the relative composition diagram allows one to decrease the nodes in the network, thus decreasing the execution time. The technique is illustrated with three example problems.
Performance and stability analysis of LP‐MPC and QP‐MPC cascade control systems
Authors: Ying Chao‐Ming , Joseph Babu 
Published: April 2004

AbstractModel predictive control (MPC) is used extensively in industry to optimally control constrained, multivariable processes. For nonsquare systems (with more inputs than outputs), extra degrees of freedom can be used to dynamically drive the process to its economic optimum operating conditions. This is accomplished by cascading a local linear programming (LP) or quadratic programming (QP) controller using steady‐state models. Such a cascade control scheme (LP‐MPC or QP‐MPC) continuously computes and updates the set points used by the lower‐level MPC algorithm. While this methodology has been in use by industry for many years, its properties have not been addressed in the literature. The properties of such cascaded MPC systems are analyzed from the point of view of implementation strategies, stability properties, and economic and dynamic performance. Some theoretical results on stability are derived along with a case study involving the Shell control problem.
Smoothing methods for complementarity problems in process engineering
Authors: Gopal Vipin , Biegler Lorenz T. 
Published: April 2004

AbstractComplementarity is central to all constrained optimization problems. However, direct enforcement of complementarity conditions is difficult because of the inherent nondifferentiability associated with them. Here, a class of smoothing methods for solving the complementarity problem by using a continuation algorithm to solve nonlinear equations is studied. The applicability of smoothing methods to approximate complicated nested derivative discontinuities is investigated using simple functions with a single smoothing parameter. In addition, an equation‐based formulation for solving the phase equilibrium problem with complementarity conditions is formulated. This approach can model the appearance and disappearance of phases directly in phase equilibrium problems. Moreover, it is shown how smoothing methods can be used to solve limiting distillation cases, such as dry and vaporless trays, modeled within an equation‐based formulation.
Kinetics on a supported catalyst at supercritical, nondeactivating conditions
Authors: Clark Michael C. , Subramaniam Bala 
Published: April 2004

AbstractIntrinsic kinetic parameters are reported for the Pt/γ‐Al2O3 catalyzed geometric isomerization of 1‐hexene (Pc = 29.7 bar; Tc = 231°C) under conditions of steady catalyst activity. Deaerating the hexene feed, pretreating it in a bed of activated alumina to reduce the peroxide impurities to 2 ppm or less, and passivating the reactor surface (by silicosteel coating) reduce the formation of hexene oligomers (coke precursors) by about an order of magnitude. This, in conjunction with operation at supercritical conditions (235–304°C, 35–70 bar), results in steady isomerization activity with no measurable coke laydown. Arrhenius plots of rate constants, estimated from the steady isomerization rates, yield an intrinsic activation energy of roughly 109 kJ/mol. This value is up to twofold greater than those reported for similar reaction systems, but on a deactivating catalysts. Our results confirm that optimum conditions that maximize catalyst activity and effectiveness factor exist in the near‐critical region with catalyst activity and effectiveness factor.
Use of hydration and dissociation chemistries with the electrolyte–NRTL model
Authors: Chen Chau‐Chyun , Mathias Paul M. , Orbey Hasan 
Published: April 2004

AbstractSound theoretical understanding and accurate mathematical representation of electrolyte solution nonideality were the subject of extensive research efforts for decades. It is demonstrated that these goals can be achieved by incorporation of hydration and partial dissociation chemistries with the semi‐empirical electrolyte NRTL model. The resulting model provides a comprehensive thermodynamic framework for accurate correlation and reliable extrapolation of electrolyte solution nonideality over the entire concentration range.
Shortcut methods for nonideal multicomponent distillation: 2. Complex columns
Authors: von Watzdorf Rüdiger , Bausa Jürgen , Marquardt Wolfgang 
Published: April 2004

AbstractIn an earlier article of the authors, the rectification body method was introduced for rapidly calculating the minimum reflux of nonideal and azeotropic multicomponent separations. Here, the RBM is generalized to two important classes of complex columns: (1) columns having sidestreams, and (2) columns with one or several side‐enricher and/or side‐stripper columns. As in the case of simple columns, the method is entirely general and does not require any a priori information on the limiting pinches prevailing in the various column sections.
Synthesis of bulk solids processing systems
Authors: Wibowo Christianto , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure for the synthesis of bulk solids processing systems guides the user in an evolutionary manner to generate flowsheet alternatives to transform a solids feed with given attributes into products with desired attributes. The first step is to select a functional structure based on the primary objective of the processing system. This is followed by the selection of equipment for the functional structure. In the third step, the functional structure is expanded by adding other necessary unit operations to form a flowsheet. This is accompanied by the assignment of a suitable equipment unit to each unit operation. Storage and transportation units are then added to the flowsheet in the fourth step. Rules and heuristics to help make decisions at each step are presented, as well as simulations used to evaluate flowsheet alternatives. Design variables are identified and short‐cut models based on discretized population balance equations are used to quantify equipment performance. The procedure is illustrated with commercial examples including the production of potash, pesticide granules, aspirin and an azo dye.
Feasibility issues in linear model predictive control
Authors: Scokaert Pierre O. M. , Rawlings James B. 
Published: April 2004

AbstractThe problem of infeasibility caused by inconsistent hard state constraints in model predictive control is considered. The difficulties that may arise are analyzed, and the inherent trade‐off a controller must address at times of infeasibility is shown. From a multiobjective viewpoint, it is demonstrated that the two approaches for handling infeasibility documented in the literature have significant limitations. Two new techniques for handling infeasibility that overcome the difficulties encountered with current approaches are presented.
Improved PCA methods for process disturbance and failure identification
Authors: Wachs Amir , Lewin Daniel R. 
Published: April 2004

AbstractPrincipal component analysis (PCA) is a powerful technique for constructing reduced‐order models based on process measurements, obtained by the rotation of the measurement space. These models can be subsequently utilized for chemical‐process monitoring, particularly for disturbance and failure diagnosis. Since the standard PCA procedure does not account for the time‐dependent relationships among the process variables, this leads to poorer disturbance isolation capability in dynamic applications. A simple idea, in which the last s PCA scores are recursively summed and used to construct descriptive statistics for process monitoring, is presented. Analytically, it is shown that the disturbance resolution afforded is enhanced as a result. Resolution is improved further through the use of an algorithm that enhances the correlations between the input and output variables through optimal time shifting. An overall strategy for on‐line monitoring developed includes disturbance identification through mapping. The approach is demonstrated by two industrially relevant case studies.
Targeting procedures for energy savings by heat integration across plants
Authors: Rodera Hernán , Bagajewicz Miguel J. 
Published: April 2004

AbstractHeat integration across plants can be accomplished either directly using process streams or indirectly using intermediate fluids. By applying pinch analysis to a system of two plants, it is first shown that the heat transfer leading effectively to energy savings occurs at temperature levels between the pinch points of both plants. In some cases, however, heat transfer in other regions is required to attain maximum savings. A systematic procedure to identify energy‐saving targets is discussed, as well as a strategy to determine the minimum number of intermediate‐fluid circuits needed to achieve maximum savings. An MILP problem is proposed to determine the optimum location of the intermediate fluid circuits. The use of steam as intermediate fluid and extensions to a system of more than two plants are discussed.
Chance‐constrained model predictive control
Authors: Schwarm Alexander T. , Nikolaou Michael 
Published: April 2004

AbstractThis work focuses on robustness of model‐predictive control with respect to satisfaction of process output constraints. A method of improving such robustness is presented. The method relies on formulating output constraints as chance constraints using the uncertainty description of the process model. The resulting on‐line optimization problem is convex. The proposed approach is illustrated through a simulation case study on a high‐purity distillation column. Suggestions for further improvements are made.
Synthesis and implementation of procedural controllers for event‐driven operations
Authors: Sanchez A. , Rotstein G. , Alsop N. , Macchietto S. 
Published: April 2004

AbstractA framework is presented for synthesizing logic feedback controllers for event‐driven operations, which are used typically for startup and shutdown operations, emergency procedures, and alarm handling. The framework encompasses techniques for discrete‐event modeling of open‐loop process behavior and operational specifications, as well as the synthesis of feedback control mechanisms called procedural controllers. A procedural controller, if it exists, is mathematically guaranteed to satisfy its operational specifications. This is of particular importance for control systems in which high integrity and correctness are required by design (such as systems in which human life is at risk). The notions introduced and the framework presented are illustrated with a small example. The applicability of the framework to cases of industrial complexity is demonstrated by synthesizing a procedural controller and implementing it as a control code for a section of the operation of an automated multipurpose‐multiproduct batch pilot plant.