bluuebunny/crossref_metadata_2025_split huggingface dataset:
Implicit model checking of logic‐based control systems
Authors: Park Taeshin , Barton Paul I. 
Published: June 2004

AbstractIncreasing automation in the CPI has led to the growing use of logic‐based control systems (or safety interlock systems) in safety‐related and sequencing operations. The growing complexity and safety‐critical nature of typical applications make developing technologies for the formal verification of logic‐based control systems with respect to their functionality a crucial and urgent issue. It still remains elusive to analysis, primarily due to the exponential growth of the alternatives that must be examined with application size. Implicit model checking is a formal verification technology that can be applied to the verification of large‐scale logic‐based control system. Its primary advantage is to formally verify large‐scale coupled systems, where a novel and compact model formulation makes tractable previously inaccessible problems. Logic‐based control systems are represented compactly as an implicit Boolean state‐space model, and the properties to be verified are represented in the language of temporal logic. Verification is posed as a Boolean satisfiability problem and then transformed into its equivalent integer programming feasibility problem, which allows for efficient solution with standard branch‐and‐bound algorithms. Benefits of the methodology are demonstrated by applying to largescale industrial examples.
Measure of closed‐loop nonlinearity and interaction for nonlinear chemical processes
Authors: Guay M. , McLellan P. J. , Bacon D. W. 
Published: June 2004

AbstractA new approach for assessing nonlinear interaction effects and closed‐loop nonlinearity in multivariable processes is presented. It is based on a differential geometric interpretation of the relative gain array that leads naturally to systematic procedures for describing interaction effects of higher order and for assessing closed‐loop nonlinearity effects in nonlinear processes. Two types of nonlinear effects associated with the behavior of a process are introduced. Between‐channel nonlinearity is associated with the nonlinear dependence of an output channel on other input ‐ output pairings. Withinchannel nonlinearity is used to identify the nonlinear effects that result from the inherent nonlinearity of an individual output channel. A root‐mean‐squared measure of nonlinearity is introduced and is used to evaluate the significance of local nonlinear effects. Nonlinear interaction measures are derived that provide tools for assessing input ‐ output pairings in a nonlinear process. This new approach extends the standard techniques and provides an estimate of the effect of nonlinearity on closed‐loop interactions.
Bridging the gap between heuristics and optimization: Capacity expansion case
Authors: Liu Ming Long , Sahinidis Nikolaos V. 
Published: June 2004

AbstractThe competition between heuristic and optimization approaches for process synthesis and process operations problems has caused major controversy in recent years. Heuristics offer fast solutions but no guarantee of optimality. Mathematical programming approaches, on the other hand, offer rigor but suffer from combinatorial explosion of computational requirements. The use of analytical investigations is proposed as a theoretical means to characterize the behavior of heuristics and optimization algorithms and produce a framework that combines the strengths of the two approaches while eliminating their weaknesses. The approach contrasts and complements the current practice in process systems engineering, which is entirely empirical in nature. The proposed paradigm is demonstrated in the context of the multiperiod capacity expansion problem for chemical process networks, a problem having much in common with both process synthesis and operations problems. Analytical investigations for this problem lead to the development of a heuristic that is proved to be asymptotically optimal under standard assumptions about the problem parameters. In the more general context of process synthesis and operations, analytical investigations present a large array of opportunities.
Modeling and control of multivariable processes: Dynamic PLS approach
Authors: Lakshminarayanan S. , Shah Sirish L. , Nandakumar K. 
Published: June 2004

AbstractThe issue of modeling and control of multivariable chemical process systems using the dynamic version of a popular multivariate statistical technique, namely, projection to latent structures (partial least squares or PLS) is addressed. Discrete input‐output data are utilized to construct a projection‐based dynamic model that captures the dominant features of the process under study. The structure of the resulting model enables the synthesis of a multiloop control system. In addition, the design of feedforward control for multivariable systems using the dynamic PLS framework is also presented. Three case studies are used to illustrate the modeling and control of multivariable linear and nonlinear systems using the suggested approach.
Ozone transfer with optimal design of a new gas‐induced reactor
Authors: Hsu Yung‐Chien , Huang Chyuan‐Jih 
Published: June 2004

AbstractThe optimal geometric design and the mass transfer of ozone for a new gas‐induced reactor characterized by the installation of a draft tube and dual pitched‐blade turbines were studied. Geometric factors including the impeller diameter, the length and diamter of draft tube, the liquid level, and the impeller speed were investigated to find the optimal gas utilization rate and power consumption for agitation. Furthermore, under the optimal geometric conditions, several variables including the impeller speed, the input gas flow rate, and the liquid level were investigated to reveal the volumetric masstransfer coefficient of ozone. The optimal geometry was suggested by three empirical equations that correlated successfully the onset impeller speed for gas induction and the power consumption post gas induction with geometrical factors and operational variables. Volumetric mass‐transfer coefficients of ozone were 0.8–1.2 min−1 under optimal geometric and proper operational conditions, which are comparable to the cited values in the literature.
Temperature‐dependent behavior of polyethylene oxide in papermaking suspensions
Authors: Khoultchaev Kh. Kh. , Kerekes R. J. , Englezos P. 
Published: June 2004

AbstractThe adsorption of polyethylene oxide (PEO) on chemi‐thermo‐mechanical pulp (CTMP), clay, and chalk suspensions was investigated at 303 and 343 K. These conditions corresponded to points below and above the critical solution temperature (CST) of a 0.005 mass % polyethylene oxide solution in the presence of 2 mol/L of KCl. The PEO adsorption on CTMP and clay particles was also studied at different initial PEO concentrations up to 50 mg/L. PEO adsorbed onto papermaking furnish particles at both temperatures, but the adsorbed amount was found to be larger above the CST in all systems. At 303 K it increased with the increase in PEO added to the system until it reached a plateau, but at 343 K it increased with the increase in PEO added in all the range of PEO concentrations up to 50 mg/L. The state of aggregation of PEO‐clay and PEO‐chalk suspensions was also studied by monitoring fluctuations in the intensity of light transmitted through the suspension. These measurements indicated a strongly temperature‐dependent aggregation. It was concluded that the entropically driven phase separation leads to enhanced aggregation, which in turn favors the retention of fiber fines and clay filler.
Pore modification using the supercritical solution infiltration method
Authors: Wang Zhaohui , Dong Junhang , Xu Nanping , Shi Jun 
Published: June 2004

AbstractWhen a supercritical (SC) solution infiltrates through micropores, its pressure will fall off considerably along the flow direction, and significant solute supersaturation can be obtained inside the pores. Thus the solid solute can deposit onto the pore surface due to nucleation. The supercritical solution infiltration (SCSI) method was applied to modify porous ceramic membranes. A mathematical model was used for the membrane poresize change during the SCSI process. Numerical solution of this model showed that for a membrane with initial pore‐size distribution (PSD), its average pore size could be increased or decreased due to dissimilar kinetics of the solute precipitation under different conditions, α‐Al2O3 microfiltration membranes were modified by the SCSI method using SC solution of the aluminum isopropoxide/propane system under different conditions. The PSD change was determined for the modified membranes after hydrolysis and sintering. With the reduction in permeability, the average pore size was reduced when the process conditions were more favorable for homogeneous nucleation and increased under the opposite conditions. Experimental results qualitatively coincided with those by the proposed model.
Screening effects when sampling suspensions in laminar flow through pores
Authors: Jones Francis J. , Weinberger Charles B. 
Published: June 2004

AbstractDilute suspensions of neutrally buoyant, uniform‐diameter spheres in a viscous liquid are sampled through pores in the wall of a stirred tank. These studies are performed to investigate screening effects near the sampling orifice that cause samples to be deficient in solids. The ratio of sphere concentration in the sample to that of the original suspension ranges from 0.08 to 1.12. Sample concentration decreases with decreasing sampling pore diameter and increasing stirring rates. The objectives of this work are both to obtain experimental relationships and to develop predictive techniques relating flow fields to sample concentration.Sample concentration is predicted by calculating particle trajectories in the region near the pore and by accounting for steric exclusion. Particle trajectories can differ from fluid streamlines due to lift forces generated in the flow field. These estimates constitute a priori predictions, since they do not rely on or introduce any empirical parameters. Predicted values of sample concentrations agree closely with data.
High‐pressure three‐phase fluidization: Hydrodynamics and heat transfer
Authors: Luo Xukun , Jiang Peijun , Fan L.‐S. 
Published: June 2004

AbstractThe phase holdups and the heat‐transfer behavior were studied experimentally in three‐phase fluidized beds over a pressure range of 0.1–15.6 MPa. Bubble characteristics in the bed are examined by direct flow visualization. Pressure effects on the bubble coalescence and breakup are analyzed mechanistically. The study indicates that the pressure affects the hydrodynamics and heat‐transfer properties of a three‐phase fluidized bed significantly. The average bubble size decreases and the bubble‐size distribution becomes narrower with an increase in pressure. The bubble‐size reduction leads to an increase in the transition gas velocity from the dispersed bubble regime to the coalesced bubble regime, an increase in the gas holdup, and a decrease in the liquid and solids holdups. The pressure effect is insignificant above 6 MPa. The heat‐transfer coefficient between an immersed surface and the bed increases to a maximum at pressure 6–8 MPa and then decreases with an increase in pressure at a given gas and liquid flow rate. This variation is attributed to the pressure effects on phase holdups and physical properties of the gas and liquid phases. A mechanistic analysis revealed that the major heat‐transfer resistance in high‐pressure three‐phase fluidized beds resides in a liquid film surrounding the heat‐transfer surface. An empirical correlation is proposed to predict the heat‐transfer coefficient under high‐pressure conditions.
Mass transfer based on chemical potential theory: ZnSO4/H2SO4/D2EHPA
Authors: Klocker Hartmut , Bart Hans‐Jörg , Marr Rolf , MÜLler Hansjourg 
Published: June 2004

AbstractA fundamental model based on chemical reaction kinetics and diffusional mass transfer for the extraction of zinc sulfate with di(2‐ethyhexyl) phosphoric acid (D2EHPA) in n‐heptane at 250 C was developed. Gradients of the chemical potential were used as the driving force for diffusion. Activity coefficients and their derivatives were calculated from the Pitzer equation in the aqueous phase, while the organic non‐ideality was considered by the Hildebrand–Scott treatment. The Nerst–Planck equation was chosen for describing the diffusion of aqueous ions, paying special care to the formation of hydrogen sulfate. It was assumed that this fast ionic reaction can be described in terms of the mass action law in the bulk and film. For the multicomponent mass transfer of the organic species, the Maxwell–Stefan theory was adopted. A kinetic equation for the extraction of zinc with D2EHPA, which considers the adsorption of the D2EHPA molecules at the interface based on the Langmuir law, was suitable for our experimental data. Organic zinc concentration vs. time was obtained in a type of Lewis cell with vibrational mixing. Molar fluxes were calculated by fitting it with rational functions, which were analytically differentiated. Initial conditions of the experiments cover a wide range of the zinc (0.1 mM to 0.05 M), D2EHPA, and sulfuric acid concentration. Experimental fluxes could be well described by this model when chemical kinetics and mass transfer were considered. In particular, the resistance to mass transfer in the organic film is important.
Dynamics of the SCR‐DeNOx reaction by the transient‐response method
Authors: Lietti Luca , Nova Isabella , Camurri Stefano , Tronconi Enrico , Forzatti Pio 
Published: June 2004

AbstractThe unsteady‐state kinetics of NH3 adsorption–desorption and of selective catalytic reduction (SCR) of NO with NH3 were studied over model V2O5/TiO2 and V2O5–WO3/TiO2 catalysts by transient response techniques. Over both catalysts the dynamic experiments could be successfully described by a kinetic model assuming (1) negligible NO adsorption on the catalyst surface; (2) nonactivated NH3 adsorption; (3) a Temkin‐type NH3 coverage dependence of the desorption energy; (4) a nonlinear dependence of the SCR reaction rate on the NH3 surface coverage. Thus, the results are supportive of an Eley‐Rideal mechanism for the SCR reaction and of a significant heterogeneity for adsorption–desorption process and surface reaction of the catalyst surface. The binary and ternary catalysts exhibit similar acid properties, but different activity in the SCR reaction, possibly related to the superior redox properties of the WO3‐containing sample. Over both samples the estimates of the activity energies for NH3 desorption at zero coverage and for the surface reaction of NO with NH3 are similar and in the 23–26 and 14–16 kcal/mol ranges, respectively.
Mathematical model of a pneumatic conveying dryer
Authors: Fyhr Christian , Rasmuson Anders 
Published: June 2004

AbstractA model for a pneumatic‐conveying dryer is presented, with the focus on the superheated steam drying of wood chips, although it can also be used for other porous materials and drying media. It includes a comprehensive 2‐D model for the drying of single wood chips, which accounts for the main physical mechanisms occurring in wood during drying, including coupled transport of water, air, vapor and heat. This model allows for features such as initial condensation and flashing at the outlet, as well as the falling rate period when the drying is controlled by internal transport. External drying conditions in the dryer are calculated by applying mass, heat and momentum equations for each incremental step in dryer length. A plug‐flow assumption is made for the dryer model, and single‐particle and dryer models were solved iteratively. The irregular movement and nonspherical shape of wood chips are accounted for by measuring drag and heat‐transfer coefficients.Model calculations illustrate the complex interactions among steam, particles, and walls that occur in a flash dryer. The drying rate, the slip velocity, and temperature vary in a complex manner through the dryer, necessitating the use of a comprehensive single‐particle model, as in this case. Previous experimental data on the drying of bark chips in a pilot dryer was used to verify the model. The predicted temperature and pressure profiles, as well as the final moisture content of the material, agreed well with the measurements. Thus, the model provides a useful tool for the design and scale‐up of pneumatic‐conveying dryers. Effects of steam and material properties on the drying were investigated with different design parameters.
Experimental study of the flow in the metering nip of a metering‐size press
Authors: Réglat O. , Tanguy P. A. 
Published: June 2004

AbstractThe metering operation in the transfer‐roll coating process is crucial for achieving a good uniformity and suitable thickness of the coating film. Experimental results carried out on a laboratory coater are reported. This coater mimics industrial flow conditions: it has a transfer roll and a metering‐rod diameter similar to those found on a pilot coater, it operates at commercial speed, and the cover of the transfer roll is deformable. The experimental apparatus is described first. Then, a video analysis of the rib pattern is presented. Some interesting features are shown, in particular the existence of an inertia regime at high speed. The nip flow hydrodynamics are investigated using measurements of the pressure profile. It is shown that the film stability is strongly linked to the flow at the exit of the nip. The analysis of the maximum pressure in the nip, for various fluid viscosities and operating parameters, is represented using a master curve.
Polymer‐solute diffusion and equilibrium parameters by inverse gas chromatography
Authors: von Meien Oscar F. , Biscaia Evaristo C. , Nobrega Ronaldo 
Published: June 2004

AbstractInverse gas chromatography (IGC) was used to measure diffusion and thermodynamic parameters of volatile compounds in polymers. A comprehensive model for IGC is proposed, and a numerical solution for it is developed. Four capillary columns were prepared using PDMS and EPDM as the stationary phase. Toluene, ethanol, water, and some chlorinated compounds were the probes for the chromatographic experiments. Limitations of the IGC technique, although not reported in the literature, are explained. Nevertheless, the results for the systems chosen were satisfactory and agreed with the literature. The effect of adsorption on the column wall is important when water is used as a solute. The adsorption effect was incorporated into the model. The parameters obtained for water using the modified model became more reliable. The parameters obtained with IGC were used to get further understanding of the pervaporation process.
Effect of the flow rates in linear, ideal, simulated moving‐bed chromatography
Authors: Zhong Guoming , Smith Maureen S. , Guiochon Georges 
Published: June 2004

AbstractThe algebraic solution for linear, ideal simulated moving‐bed (SMB) chromatography derived previously revealed important new properties of the SMB process. This solution was validated by comparing with experimental data and with the results of numerical solutions of the equilibrium–dispersive and the lumped kinetic model. This earlier solution, however, was limited to the simple case in which the safety factor was assumed to be the same for the flow rates in all four sections. An extension of this solution to the case in which the safety factors differ and allow an independent selection of the four different flow rates (within limits) is derived. This solution accounts well for most practical situations. It permits the discussion of the influence of different flow rates on the performance of an SMB unit, an issue of critical importance for the optimization of the design and operation of these separators.
Optimal alarm logic design for mass‐flow networks
Authors: Tsai Chii‐Shang , Chang Chuei‐Tin 
Published: June 2004

AbstractAn optimal alarm‐system design method, which takes full advantage of the inherent hardware and spatial redundancies in a mass‐flow network, is proposed. In particular, systematic procedures are developed to identify independent measurement methods for the flow rate of any stream in the process and to synthesize corresponding alarm generation logic. To implement the suggested alarm strategy, the formulas for evaluating conditional probabilities of type I and II mistakes are also derived. The results of applying the proposed alarm system to the application example show that the approach taken in this work is effective in suppressing the latter mistakes. Further, this system is superior to any of the existing alarm techniques in the sense that it can be appropriately tailored to minimize the expected loss due to misjudgments in generating alarms.
Effect of the membrane activity on the performance of a catalytic membrane reactor
Authors: Coronas J. , Gonzalo A. , Lafarga D. , Menéndez M. 
Published: June 2004

AbstractA mathematical model for a catalytic membrane reactor for oxidative coupling of methane (OCM), in which the membrane acts as an oxygen distributor to a bed of catalyst, is presented. From experimental data obtained using several silica membranes impregnated with Li and/or Na, which were prepared by the sol–gel method using alumina supports, the catalytic activity of the membrane was included in the so‐called real membrane reactor (RMR) model. Then, the RMR performance was compared with that of the ideal membrane reactor (IMR), whose membrane was supposed to have no activity for the OCM and with experimental data obtained in membrane reactors. Since the membrane activity was implemented in the RMR model, for the first time in the literature, maxima in the hydrocarbon selectivity–methane conversion curves were predicted in agreement with previous experimental trends. Besides, the IMR performance was compared with that of the fixed‐bed reactor (FBR), giving the maximum improvement of a membrane reactor over the FBR. Key factors for the future improvement of the performance in this kind of membrane reactor are deduced from these simulations.
Coal liquefaction mechanism using a tritium tracer method
Authors: Godo Masazumi , Umemura Masatsune , Ishihara Atsushi , Kabe Toshiaki 
Published: June 2004

AbstractTo determine the behavior of hydrogen in tetralin, the reaction of tetralin with tritiated gaseous hydrogen was studied in a flow reactor at 400–450°C, 2.5–9.8 MPa for various residence times. The amount of hydrogen exchange between tetralin and tritiated hydrogen was estimated from the balance of hydrogen and tritium. Although yields of methylindan and naphthalene, and the hydrogen‐exchange ratio (HER) of tetralin increased monotonously with residence time, these values were scarcely influenced by the reaction pressure at every temperature. It was thought that the formation of tetralyl radicals in this system would be the rate‐determining step for both the conversions of tetralin into methylindan and naphthalene, and the hydrogen exchange of tetralin. Conversions of tetralin into methylindan and naphthalene, and the hydrogen‐exchange reaction using the autoclave were very close to those using the flow reactor.