bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic operation of butadiene dimerization reactor undergoing catalyst deactivation
Authors: Dixit Ravi S. , Grant Nancy
Published: March 2009

Operation of fixed‐bed catalytic reactors undergoing catalyst deactivation has been investigated as an optimal control problem to yield optimal temperature policies. An efficient numerical scheme using a control vector iteration method based on gradients in functional space is developed. The procedure is applied to develop optimal temperature profiles for a butadiene dimerization process. The temperature‐time trajectories and dynamic activity profiles are strongly influenced by kinetics. A sensitivity analysis is done to study the effect of flow rates, conversion level and parameters that influence kinetic and deactivation processes. These results have been validated with experimentation on a lab scale reactor and a 9.14 m pilot‐plant reactor.
Catalytic SO2 oxidation in a periodically operated trickle‐bed reactor
Authors: Lee Joong Kee , Ferrero Stefano , Hudgins R. R. , Silveston P. L.
Published: March 2009

CentaurTM carbon (Calgon Carbon Corp.) was used as a catalyst for SO2 oxidation in a trickle bed under periodic interruption of its liquid flow for cycle periods from 15 to 60 min, cycle splits (split being the proportion of a cycle in which liquid flows) from 0.0083 to 0.2, and feed temperatures about 80°C.

SO2 removal in the trickle bed was improved at longer periods. At a fixed period of 15 min, a maximum occurred with split. At high splits, platinized and unplatinized carbons performed indistinguishably. Results suggested kinetic rate control at low splits and oxygen mass transport control at high splits.
The transient operation of a solid oxide fuel cell monolith under forced periodic reversal of the flow
Authors: Neophytides S.G. , Tripakis A.
Published: March 2009

The forced periodic reversal of the flow is proposed for the case of a Solid Oxide Fuel Cell (SOFC) monolith. A one‐dimensional non‐steady state heterogeneous model is applied to an investigation of H2 electrochemical oxidation in a co‐current flow solid oxide monolithic fuel cell. Results are reported on the transient evolution along the reactor, of the species conversion, temperature distribution, thermodynamic energy conversion efficiency and volumetric power density. This novel transient operation of an SOFC leads to improved and highly efficient performances, thus allowing for a combination of the concepts of a regenerative heat preheater and of an electrocatalytic converter, in a single SOFC monolithic assembly.
The STAR configuration for methanol synthesis in reversed flow reactors
Authors: Vanden Bussche K. M. , Froment G. F.
Published: March 2009

Although the transient reversed flow operation of a fixed bed reactor for methanol synthesis was shown to be an economically attractive alternative for the traditional steady state technology, it suffers from strongly varying exit concentrations upon flow reversal. These not only disturb the operation of downstream equipment but also significantly decrease the time averaged conversion to methanol.

To avoid this drawback, the STAR reactor concept is introduced. It operates in a fully transient mode, but combines the attractive features of the reversed flow reactor operation with practically constant exit concentrations. Extensive simulation work shows that the conversions obtained exceed those of the single reversed flow reactor by at least 5 percent.
Extension of EOS non‐iterative methods to density calculations: Correlation of saturated molar volumes and heats of vaporization
Authors: Zabaloy Marcelo S. , Vera Juan H.
Published: March 2009

Soave's direct calculation procedures for the vapor pressure of pure compounds with cubic equations of state (EOSs), have been extended to the calculation of phase densities at saturation for Peng‐Robinson (PR) type EOSs. These universal relations have been used to propose EOS‐based correlation methods for the pure compound saturated liquid and vapor molar volumes, at temperatures higher than the normal boiling point. The methods yield satisfactory results independently of the molecular nature of the chemical under consideration. The results for phase densities are used to correct the heats of vaporization predicted by the ZVPR‐EOS. Complete relative error information is provided for calculated heats of vaporization and correlated vapor and liquid phase molar volumes for more than one hundred compounds of industrial interest.
Factors influencing the efficacy of an interfacial modifier for the interface in an immiscible polymer blend
Authors: Favis Basil D. , Cigana Patrick , Matos Mireya , Trembla Alain
Published: March 2009

The modification of the interface in immiscible polymer blends is critical in order to optimize physical properties. Despite the great commercial importance of polymer blends, many aspects of the emulsification process remain unclear In this paper, it will be shown that an emulsification curve can be used to estimate the influence of the architecture molar mass of styrene/hydrogenated butadiene block copolymer interfacial modifiers on the emulsifion of polystyrene/ethylene‐propylene rubber blends under melt processing conditions. An expression for eing the critical amount of copolymer to saturate the interface, as well as aspects concerning the localisation of the modifier in the blend system will also be addressed.
The catalytic oxidative coupling of methane: II. Axial gas sample probing in a bubbling Fluidised‐Bed reactor and the effect of side reactions
Authors: Do K. T. , Edwards J. H. , Tyler R. J.
Published: March 2009

The atmospheric pressure catalytic oxidative coupling of methane was studied in detail by axial gas concentration probing experiments in a 60 mm OD bubbling fluidised‐bed reactor system. Experimental data demonstrated a very fast reaction which occurred within the vicinity of the distributor (normally in the first 5 mm of bed height) under normal reaction conditions of 850°C and 83 vol%/17 vol% CH4/O2 feed. The data also showed that hydrocarbon selectivity was deleteriously affected by side reactions which were also promoted by the catalysts even though they were good catalysts for the oxidative coupling reaction. If this reduction in hydrocarbon selectivity is inevitable then there will be optimum operating conditions for each catalyst in the bubbling fluidised bed reactor.
Kinetics of iodine poisoning of hydrophobic Pt/SDBC catalyst for hydrogen isotopic exchange reaction
Authors: Wei Yue‐Zhou , Shimizu Masami , Takeshita Kenji , Kumagai Mikio , Takashima Yoichi
Published: March 2009

Changes with time in the isotopic exchange reaction rate between H2 and HDO(v) over a hydrophobic Pt/SDBC (styrene‐divinylbenzene copolymer) catalyst induced by iodine have been studied experimentally. The addition of a trace amount of I2 to the reactor caused a remarkable decrease in the activity of the catalyst. The measurement results by means of the gas chromatographic pulse technique show that the H2 adsorption onto the catalyst surface was strongly inhibited by iodine. A kinetic model for the poisoning was developed in terms of the competitive adsorption of I2 with H2 onto the catalytic active site. The experimental results were explained reasonably by the proposed kinetic model based on the site balance by assuming that I2 adsorbs non‐dissociatively on the active site. The poisoning could be prevented by the conversion of I2 to I− or IO3−through redox reactions.
Arma neuron networks for modeling nonlinear dynamical systems
Authors: Krishnapura Venugopal G. , Jutan Arthur
Published: March 2009

A new neuronal structure, the ARMA neuron, is proposed here. These new neurons are designed for modeling nonlinear dynamics often encountered in chemical engineering processes. They are an extension of standard neurons which are used for static process modeling. These new neurons contain internal input/output dynamic structure and can model dynamic non‐linearities in a flexible manner. A nonlinear output transformation is used here as opposed to a linear version used earlier (Krishnapura and Jutan, 1993). New algorithms for training networks comprised of the new ARMA neurons are developed using the backpropagation approach. The ARMA neurons are used to model both simulated and experimental nonlinear dynamic processes, including an industrial fluidized bed reactor.
Investigation of the oxidation of o‐Xylene over a Vanadia/Titania catalyst by means of the TAP reactor
Authors: Creten Glenn , Froment Gilbert F. , Kopink Frank‐Dieter
Published: March 2009

The oxidation of o‐xylene over a commercial V2O5/TiO2 (anatase) catalyst was studied in the TAP (Temporal Analysis of Products) reactor system. The transient method with high time resolution has led to new insights into the reaction mechanism. The selective oxidation is shown to consist of a sequence of steps, involving intermediates which desorb as o‐toluolaldehyde and phtalide. The key reaction step in the non‐selective oxidation is shown to be a decar‐bonylation of a surface species, leading to a surface benzoate. The kinetics of the elementary steps in the reaction were derived from a quantitative analysis of the transient responses on o‐xylene pulses.
Biological purification of exhaust air containing toluene vapor in a filter‐bed reactor
Authors: Bibeau L , Heltz M. , Kiared K. , Leroux A. , Brzezinski R. , Viel G.
Published: March 2009

Experiments during a period of 93 days are reported on the treatment of waste air containing toluene vapor using a laboratory scale biofilter system packed with peat inoculated with specific florae (Pseudomonas type) and intermittently humidified with a nutrient solution necessary for the survival of the micro‐organisms. Design and operation parameters were regularly measured in order to check the performance of the biodegradation process.

Under pseudo‐steady state conditions, a maximum elimination capacity of 70 g/m3.h was obtained for an inlet load of 190 g/m3.h. Elimination capacity data obtained agreed well with the predictions of two recognized zero order kinetic models. Also, the biofilm thickness as predicted from the Ottengraf and van den Oever model (1983) was around lmm.
A simple method of estimating surface reaction rates by moment analysis of tap reactor pulse experiments; application to benzene hydrogenation
Authors: Lafyatis David S. , Creten Glenn , Dewaele Olivier , Froment Gilbert F.
Published: March 2009

A method of estimating the lifetime of surface reaction intermediates by moment analysis of TAP reactor pulse response curves has been developed. The average surface lifetime of the adsorbed reaction intermediate in the hydrogenation of benzene to cyclohexane over Pt/SiO2 at 140°C and 92 kPa of hydrogen is 38 ± 4 ms, as measured by a TAP pulse experiment. The steady‐state turnover frequency for this reaction under the same conditions is 1.0 ± 0.2 s−l. This implies that the surface coverage of Pt by benzene is low under the steady‐state conditions.
Evaluation of a novel self‐aerating, oscillating baffle column
Authors: Mackley M. R. , Stonestreet P. , Thurston N. C. , Wiseman J. S.
Published: March 2009

We describe the operation of a pilot scale oscillating baffle column using a self‐aeration system for oxygenation of water. The top baffle has a high constriction ratio and is sufficiently near to the surface of the water such that gas bubbles are generated. This aeration plate is coupled with a series of equally spaced low constriction orifice baffles, which lead to uniform dispersion of entrained air bubbles throughout the liquid volume. Flow visualisation experiments using video and still photography were used to identify two mechanisms for bubble generation: bubble formation under the water surface by surface vortex suction, and bubble generation from the collapse of a surface fountain and subsequent entrainment of bubbles into the bulk. Mass transfer measurements have shown that under most conditions a uniform oxygen concentration could be obtained throughout the column as a result of efficient mixing, and that the sole limitation to mass transfer performance was determined by the aeration mechanism. Initial comparison on the basis of aeration efficiency with other devices reveals a modest oxygen transfer rate, but with low specific power consumption of order 0.3 kW/m3.
Numerical flow simulation of viscoplastic fluids in annuli
Authors: Meuric Olivier F. J. , Wakeman Richard J. , Chiu Tak W. , Fisher Kenneth A.
Published: March 2009

This paper describes numerical solutions for the laminar flow of non‐Newtonian fluids in vertical annuli using the Herschel‐Bulkley model to describe the rheological behaviour of such materials. Numerical solutions have been obtained when there is both axial and tangential flows in either a concentric or eccentric annulus. The tangential flow arises from the rotation of the inner cylinder of the annulus and the axial flow from a constant axial pressure gradient. The flow is analysed by solving the momentum and continuity equation numerically using the finite element method. The dimensionless velocity, deformation and stress profiles with other quantities such as the apparent viscosity and pressure distribution have been calculated for various eccentricities, radius ratios, fluid properties and flow parameters; the results give insights into the flow behaviour in the annuli. It is shown that the inclusion of rotational effects, for a fixed pressure gradient, is likely to increase the axial volumetric flowrate over non‐rotating situations in concentric geometries. New results reveal that, in eccentric annuli, the situation is reversed and the flowrate gradually decreases as the rotation rate is increased.
A stochastic model for the simulation of the natural flow in random packed columns
Authors: Song M. , Yin F. H. , Chuang K. T. , Nandakumar K.
Published: March 2009

A stochastic model has been developed to simulate the “natural flow” and the spatial evolution of flow patterns in the downstream direction in randomly packed beds. The natural flow is defined as the tendency of liquids flowing down a packed bed to redistribute radially in a natural fashion. A column of 0.5 m diameter with 25 mm Pall rings is selected to test the model. The simulation results of flow distributions are in good agreement with available experimental data from the literature. Unlike the existing models, our approach can simulate liquid flow distributions for different realizations of random packings.
Investigation of the mean and turbulent particle velocity fields in a spouted bed using radioactive particle tracking
Authors: Djeridane Toufik , Larachi Faïçal , Roy David , Chaovki Jamal , Legros Robert
Published: March 2009

A non invasive experimental Radioactive Particle Tracking method (R.P.T.) was used to determine the three‐dimensional mean and turbulent particle velocity fields in a spouted bed. The local statistical properties were evaluated with approximately one million data obtained on typically 6 hours of particle tracking. Radial profiles of first and second order moments of the particle velocity field are presented in the spout, the annulus and the fountain region on several axial sections. In addition to the complete description of the solids mean flow pattern, the relevance of a strong anisotropy behavior for particle turbulence field was well established. Thus, this study constitutes an original experimental investigation needed both for a better physical understanding and refined flow modelling of gas‐solid flows in spouted beds.
Quantification of laminar mixing in the kenics static mixer: An experimental study
Authors: Jaffer Shaffiq A. , Wood Philip E.
Published: March 2009

The laminar flow field in a Kenics KM static mixer has been studied using laser induced fluorescence and digital image analysis. Mixing was quantified by measurement of the number average striation thickness, variance of striation widths and interfacial area, for elements of length to diameter (L/D) ratios of 0.8, 1.0, 1.5 with 90° twist per element. From flow visualisations, transitions were observed in the flow where vortices developed above the first and second elements at Reynolds numbers of 43 and 90 for L/D = 0.8 and Reynolds numbers of 55 and 105 for L/D = 1.0. It was found that these vortices did not appreciably enhance mixing based on striation thickness and variance of striation widths measurements after 4 to 5 elements. The influence of viscosity ratio showed a viscosity ratio (dyed stream/bulk stream) of I had faster interfacial area growth and created more uniform mixtures compared to a viscosity ratio of 0.2 for flow rate ratio of 0.2.
Determination of the mixing performance of sulzer SMV static mixers by laser induced fluorescence
Authors: Karoui Asma , Hakenholz Frédéric , Le Sauze Nathalie , Costes Jean , Bertrand Joël
Published: March 2009

Local concentrations are measured at the outlet of different configurations of Sulzer SMV static mixers placed in a tube. Laser Induced Fluorescence is the non intrusive technique used to measure mean and RMS concentrations. The two fluids mixed are miscible and the flow regime is turbulent. The influence of the number of elements, their position and the ratio between the velocities of the two compounds on the mixing is studied. The results show that these parameters are important for the quality of mixing. The velocity ratio influences the radial mixing, while the mixing length depends on the number and position of the elements.
Natural convection in a porous medium at high rayleigh numbers — application of prandtl's analogy
Authors: Rao Vedula Dharma , Naidu Sureddy V. , Sarma Pullela K.
Published: March 2009

The problem of natural convection heat transfer from an isothermal vertical cylinder to a saturated porous medium is solved by the integral method making use of one‐seventh profiles for velocity and temperature variation in the boundary layer. Prandtl's analogy is used to obtain the wall heat transfer coefficients. The results obtained for Rayleigh numbers greater than 109 and Prandtl numbers 4 and 0.12 are compared with experimental data from literature show satisfactory agreement. Also an approximate closed form solution is presented for the case of a flat wall to predict local Nusselt numbers.
Selective kinetic deactivation model for methanol synthesis from simultaneous reaction of CO2 and CO with H2 on a commercial copper/zinc oxide catalyst
Authors: Rahimpour Mohammad Reza , Fathikalajahi Jamshid , Jahanmiri Abdolhosein
Published: March 2009

A kinetic model for the deactivation of copper/zinc oxide catalyst during the methanol synthesis has been developed. This model is of the Langmuir‐Hinshelwood‐Hougen‐Watson type and considers two types of active sites for the deactivation of catalyst. One of the site types on copper is allocated for the deactivation of the catalyst due to carbon dioxide while another type is assigned for the deactivation of the catalyst due to carbon monoxide. The parameters of the deactivation rate equations based on the above concept have been determined using the experimental data of Hoffmann (1993). The validity of the deactivation model has been checked by comparing the results predicted by the model with experimental data different than of those used to evaluate the parameters of the model. The good agreement that noticed in this comparison confirmed the idea that CO and CO2 are responsible at different extent for the deactivation of Cu/ZnO catalyst during methanol synthesis.
A method of evaluating limestone reactivity with SO2 under fluidized bed combustion conditions
Authors: Mattisson Tobias , Lyngfelt Anders
Published: March 2009

The reactivity of limestone with sulphur dioxide has been evaluated during conditions similar to those existing in a fluidized bed combustor using a fixed‐bed quartz reactor. The reactivity of up to 11 particle sizes of 2 limestones were evaluated, and an exponential decay function was found to best describe the rate behaviour versus conversion of CaO to CaSO4. The two constants in the exponential decay approximation could both be expressed as functions of particle size. Subsequently, the limestone reactivity as a function of both size and conversion could be reasonably well described by a total of 4 to 6 constants. An analytical sulphur capture model for fluidized bed boilers (FBB) that incorporates this type of reactivity function is proposed.
Faradaic processes on activated carbon particles: Example of sulfite anodic oxidation
Authors: Balduf Torsten , Valentin GÉRard , Lapicqve François
Published: March 2009

Activated carbon has often been reported as a suitable material for numerous applications e.g. energy storage, batteries and pollution control, due its high adsorption capacity allowed by its high surface area. Besides, activated carbon can also be used for the chemical transformation of matter through faradaic processes. This paper deals with the performance of activated carbon (AC) particles as an electrode material for the anodic oxidation of sulfite and bisulfite species into sulfate. The oxidation was carried out at the surface of a packed‐bed of AC particles (volume 170 cm3); the main operating conditions, namely potential and solution pH were varied. The sulfate production was shown to be controlled by the electrode kinetics and the internal transfer in the carbon pores. Interactions between the capacitive phenomena, occurring in the electrical pretreatment, and the faradaic processes were discussed.
Batch reactor control using a multiple model‐based controller design
Authors: Krishnan Arun , Kosanovich Karlene A.
Published: March 2009

This work presents the development of a model‐based controller design called Multiple Model Predictive Control (MMPC) based on a set of linear, time‐varying, state space models to regulate batch processes according to multiple, pre‐specified reference profiles. Sufficient conditions for stability and boundedness of the dynamic evolution of the forced nonlinear system are provided. The performance of the MMPC design is demonstrated on a model of a batch reactor that represents the production of a polymer product.
Kinetics and reaction mechanism of catalytic oxidation of low concentrations of hydrogen sulfide in natural gas over activated carbon
Authors: Dalai Ajay K. , Tollefson Eric L.
Published: March 2009

The kinetics of the hydrogen sulfide oxidation process, producing mostly sulfur and water, was studied using 0.25 to 1.0 g Hydrodarco activated carbon catalyst and varying the O2/H2S ratio (molar basis) in the feed gas between 0.5 to 0.6 in the temperature, and pressure ranges from 125 to 200°C and 225 to 780 kPa. SO2 was obtained as an undesirable by‐product during H2S oxidation reaction or as a product during regeneration of the catalyst. The feed gas contained 0.9 — 1.3 mol% H2S with approximately 80 mol% CH4. In this paper, the factors affecting the H2S conversion and SO2 formation are presented. The rate expressions for (a) H2S conversion and (b) SO2 formation were developed from the Langmuir‐Hinshelwood surface control reaction model. The experimental data were well correlated by the rate equations. Also, the rate parameters were evaluated and correlated with temperature. The activation energies for H2S oxidation and SO2 production reactions were calculated to be 34.2 and 62.5 kJ/mol, respectively. Partial pressures of oxygen and H2S were found to influence H2S conversion whereas, the presence of water in the feed gas up to 10.5 mol% did not affect H2S conversion significantly. Heats of adsorption for various species on the active sites were calculated. SO2 production was, as expected, enhanced at higher temperature, and its rate was much smaller than the oxidation rate of H2S under the reaction conditions used.
Fabrication of amperometric biosensors by entrapment of enzymes in functionalized polypyrrole films
Authors: Cosnier Serge
Published: March 2009

The concept and potentialities of an original electrochemical procedure of enzyme immobilization are described. This two‐step method consists of the adsorption of an aqueous amphiphilic pyrrole monomer‐enzyme mixture on an electrode surface followed by the electropolymerization of the adsorbed monomers. This procedure is compared with the conventional electrochemical methods of biosensor construction. Several bienzyme electrodes devoted to the improvement of the biosensor selectivity or to the amplification of the biosensor sensitivity are described. In addition, examples of organic phase enzyme electrode and the electrical wiring of immobilized enzymes are presented.
The efficiency of short airlift pumps operating at low submergence ratios
Authors: Lawniczak Fabrice , Francois Pierre , Scrivener Olivier , Kastrinakis Eleftherios G. , Nychas Stavros G.
Published: March 2009

An airlift pump operating at submergence ratios between 0.2 and 0.6 and using water as the pumping liquid, has been investigated. Circular pipes of constant short length of 1 m and inner diameters of 3 and 5 cm were used as riser tubes. The water flow rate measurements for various air flow rates allowed the study of the pumping efficiency as a function of the air flow rate, submergence ratio and certain geometrical parameters (riser tube diameter and injector design). The efficiency curves start from a zero efficiency at a minimum air flow rate, then increase rapidly with the air flow rate up to an efficiency maximum. For higher air flow rates, the efficiency decreases exponentially. Diagrams showing the influence of the riser tube diameter and injector design, are presented. Additionally, based on the experimental data, two equations are presented, which allow the prediction of the maximum efficiency and the corresponding water and air flow rates inside the experimental range.
Two dimensional flow deflection screen model
Authors: Oshinowo Lanre , Kuhn David C. S. , Charles Michael E.
Published: March 2009

A flow deflection screen model is proposed and implemented to predict the influence of expanded metal screens on a turbulent wind tunnel flow. The screen model successfully predicted the mean velocity and turbulence distribution in the flow field downstream of different screen types and orientation in the wind tunnel flow.
The influence of particle size and density on the radial gas mixing in the dilute region of the circulating fluidized bed
Authors: Mastellone Maria Laura , Arena Umberto
Published: March 2009

A cold model of a CFB, having a 0.120m ID, 5.75m high riser, was operated at a superficial gas velocity of 6m/s and at average solids mass fluxes varying in the range between 16 and 55kg/sm2. A stream of carbon dioxide was injected continuously at a fixed position along the riser axis and used as tracer gas. Three solids, belonging to groups A and B of Geldart's classification, were selected in order to investigate separately, the effect of particle size and density on the radial mixing of the gas phase. The intensity of radial gas dispersion reduced when larger or heavier particles were used. The differences in the values of radial dispersion coefficient and Peclet number were explained, taking into account the role of the particle size with respect to the scale of gas turbulence.
Chaotic characteristics of local voidage fluctuation in a circulating fluidized bed
Authors: Ohara Hiroaki , Ji Hongshen , Kuramoto Koji , Tsutsumi Atsushi , Yoshida Kunio , Hirama Toshimasa
Published: March 2009

Local voidage fluctuations have been measured by using an optical transmittance probe at various axial and radial positions in a circulating fluidized bed riser with a 0.1 m i. d. and 10 m height. The chaotic time series analysis of the local voidage fluctuations has been adopted to characterize the nonlinear dynamics of the circulating fluidized bed riser. The variations of the correlation dimension and the Kolmogorov entropy of the voidage fluctuation were found to depend on the local time‐average voidage. The axial and radial distributions of the correlation dimension and the Kolmogorov entropy were strongly affected by the solids flow structures (e.g. core‐annulus flow) in various operating conditions. The correlation dimension of local voidage fluctuations increases along the riser, except the position near the distributor. Both, the correlation dimension and the Kolmogorov entropy of local voidage fluctuations near the wall, were found to be smaller than those at the center of the riser, independent of the solids circulation rate and the axial position.
Kinetics and mechanism of the reaction between ozone and hydrogen peroxide in aqueous solutions
Authors: Kuo Chiang‐Hai , Zhong Li , Zappi Mark E. , Hong Andrew P.
Published: March 2009

A kinetic model has been developed, taking into account both decomposition of ozone molecules and interactions between ozone and hydrogen peroxide for formation of hydroxyl radical and subsequent reactions. Experiments were carried out at 25°C in the pH range of 3 to 13, indicating that the depletion rate of ozone increases with the concentrations of ozone, hydrogen peroxide and hydroxyl ion, as predicted by the kinetic model. Adverse scavenging reactions, however, also play significant roles at sufficient concentration ratios of hydrogen peroxide to ozone and high concentrations of hydroxyl ion in reducing the depletion rate. Results of this research suggest, that it is most desirable to conduct the peroxone oxidation for pollutant destruction by the hydroxyl radical reaction in alkaline solutions of pH below 11, while maintaining about the same concentration of ozone and hydrogen peroxide.
Assessing the precision of model predictions and other functions of model parameters
Authors: Quinn Shannon L. , Bacon David W. , Harris Thomas J.
Published: March 2009

Models fitted to data are used extensively in chemical engineering for a variety of purposes, including simulation, design and control. In any of these contexts it is important to assess the uncertainties in the estimated parameters and in any functions of these parameters, including predictions from the fitted model. Profiling is a likelihood ratio approach to estimating uncertainties in parameters and functions of parameters. A comparison is made between the optimization and reparameterization approaches to determining likelihood intervals for functions of parameters. The merits and limitations of generalized profiling are discussed in relation to the linearization approach commonly used in engineering. The benefits of generalized profiling are illustrated with two examples. A geometric interpretation of profiling is used to elucidate its value, and cases are identified for which the numerical algorithm fails. An alternative approach is suggested for these cases.
Effect of the grid‐velocity on attrition in gas fluidized beds
Authors: Wu Shu‐Yii , Baeyens Jan , Chu Chen‐Yeon
Published: March 2009

Changes in particle size distribution play an important role in fluidized bed processes, and these changes are dominated by elutriation and carryover of fines and by attrition or agglomeration. In this study on attrition in gas‐fluidized beds, we found that the attrition is a function of the particle size distribution, the jet velocities and the overall superficial gas velocity. Empirical equations have been developed to predict the attrition rate.
On the scaling‐up of a two‐stage air blown entrained flow coal gasifier
Authors: Chen Caixia , Miyoshi Takahiro , Kamiya Hidehiro , Horio Masayuki , Kojima Toshinori
Published: March 2009

A two‐stage air blown entrained flow gasifier is being developed in Japan for the IGCC process. However, its scale‐up up faces significant difficulties because of ash/slag deposition problems. The ash/slag deposition in the gasifier depends on both the ash properties and entrainment produced by the swirling gas flow. Therefore, the flow hydrodynamics are critical issues for the control of the ash behavior. In this paper, a comprehensive simulation model is used to examine the effects of the gasifier geometry and jet configuration on the flow hydrodynamics in order to control the ash deposition on the gasifier walls. A swirl number for the multi‐stage injection swirling gas flow is defined and proved to be the most important hydrodynamic scaling law for the entrained flow gasifier.
Experimental study on the simultaneous adsorption of carbon dioxide and moisture from nitrogen in linde 5 a molecular sieves
Authors: Ghosal Aloke K. , Samanta Amar N. , Maiti Binoy R.
Published: March 2009

Experimental data for the simultaneous adsorption of CO2 and moisture with variations of some process variables, such as inlet adsorbate concentration, particle Reynolds number, and bed diameter to bed length ratio, have been generated to see their effects on the efficiency of adsorption of CO2 and moisture. Presence of moisture strongly affects the CO2 adsorption behaviour leading to roll up of CO2 concentration breakthrough curves, whereas the presence of CO2 has an insignificant effect on the moisture adsorption behaviour.
An explicit approximation for the wetted angle in two‐Phase stratified pipe flow
Authors: Biberg Dag
Published: March 2009

In two‐phase stratified pipe flow the wetted angle relates the flow geometry to the holdup. The relation linking the holdup to the wetted angle does not, however, have a simple explicit solution and is therefore often solved numerically. This analysis yields simple explicit approximations for the wetted angle for a given holdup, which constitute a convenient alternative to a numerical solution.
Gas mixing in a turbulent fluidized bed reactor
Authors: Sotudeh‐Gharebaagh Rahmat , Chaouki Jamal
Published: March 2009

A series of experiments has been conducted to study mixing and hydrodynamic behaviour of a downward facing sparger in a turbulent fluidized bed reactor. Using pressure measurement techniques, two flow discharge modes were identified around the sparger by injecting a gas tracer into the bed. These are bubbling and jetting conditions. Experimental results show that, under bubbling conditions, bubbles tend to keep their identity, while under jetting conditions a highly turbulent heterogeneous area is formed around the injection point. Due to attrition and erosion of internal heating or cooling surfaces in industrial reactors, the dominant discharge mode is the bubbling pattern. Therefore, in this investigation, the bubbling pattern is studied by measuring the radial and axial dispersion of gas tracer injected to a hot fluidized bed reactor of 20 cm diameter of FCC and sand particles. A three‐phase model is also proposed in order to predict the mixing length. In addition, the effect of sparger configuration on tracer gas mixing was examined for FCC particles.
Fluidized state gelation of ceramic microspheres: Feasibility study of a continuous process and analysis of the chemical dehydration phenomena
Authors: Rovero Giorgio , Vanni Marco
Published: March 2009

A continuous gelation process for producing aluminum and zirconium hydroxide microparticles was conceived and tested in a lab‐scale apparatus. Fluidized state was devised as an appropriate hydrodynamic configuration to maintain the reacting sol microdrops suspended: stable non‐coalescing spherical gel particles in a size range quite below 100 μm were produced via gelation. The microspheres produced by a subsequent calcination step showed a diameter ranging between 2 μm and 20 μm. This powder, without further size classification, was an optimal product to manufacture test specimens by sintering. Measurements on the mechanical properties, such as toughness, flexural strength and hardness, classified the test bars as a very promising ceramic material. In order to enlighten the chemical drying phenomenon and devise the main governing mechanisms acting in the gelation reaction, an extremely simplified experimental system was set. A single drop of sol was deposited into a given amount of the dehydrating liquid medium and observed by an optical microscope; image analysis permitted us to identify the gel formation, the size reduction kinetics, as well as secondary phenomena.
A model for the evaporation of water from large glass particles in pneumatic transport
Authors: Littman Howard , Day Jenn‐Yuan , Morgan Morris H.
Published: March 2009

A model is presented for the evaporation of water from large particles in pneumatic transport. The work is relevant for estimating the coating solution feed rate and the length of the draft tube in Wurster‐type particle coaters. Specifically, the rate of evaporation of water from 1 mm glass particles in a 28.45 mm tube was calculated from the model. The rate increased with solids mass flow rate, inlet air temperature and inlet particle temperature. The heat was more rapidly removed from the particle phase than from the air phase and high inlet air temperatures are tolerated. The model presupposes that the gas and particle velocities, and voidage are known and that the water film on a particle is thin and uniformly distributed. Hydrodynamic considerations that impact on the calculations are discussed.
Enhancement of the interfacial transfer of iodine by chemical reaction
Authors: Evans Greg J. , Ling Juliette R.
Published: March 2009

Enhancement of the air‐water interfacial transfer of I2 by reaction with I− was investigated in order to evaluate a mechanistic model. Separate systems for evaporation and absorption of I2 were studied. The overall mass transfer coefficient increased from 2 × 10−4 to 2.5 × 10−3 cm/s as I− concentration increased from 10−4 to 10−1 M. At I− concentrations greater than 10−1 M, the interfacial transfer of I2 was gas‐side limited. The model gave a good representation of these results.
Mixing of a lignin‐based slurry fuel
Authors: Posarac Dusko , Watkinson A. Paul
Published: March 2009

Lignin‐based slurry fuels are a potential alternative to fossil fuels in kraft pulp mills. Lignogels — mixtures of lignin, fuel oil, water and surfactant — are non‐Newtonian fluids, with shear‐thinning and thixotropic behaviour. Their mixing was investigated in tanks with volumes of 3 and 30 L. An A310 hydrofoil impeller was used in all experiments. Results were compared with measurements in Newtonian fluids, used to characterize the impeller over a broad range of Reynolds numbers (1–500 000). An aqueous CMC solution was also used for characterization of the impeller and estimation of the Metzner‐Otto constant. Results in the transition region were corrected by introduction of two empirical parameters.
Fluid‐Borne entities in the impeller stream of a rushton turbine
Authors: Glasgow Larry A.
Published: March 2009

The breakage or disintegration of suspended entities by energetic fluid motions in stirred tanks is an essential aspect of many operations in the chemical process industries. However, the hydrodynamic inhomogeneity of such tanks makes it extremely difficult to characterize the stresses experienced in any simple manner. This work provides a determination of both the location and the frequency of interaction of spherical fluid‐borne entities with the discharge of a Rushton turbine. These data show how both particle size and impeller speed affect the severity of the exposure, setting the groundwork for improved descriptions of the dynamic behaviour of the particle size distribution in a wide variety of dispersed‐phase processes.
Predictive models for the viscosities of multicomponent liquid n‐Alkane and regular solutions
Authors: Nhaesi Abdulghanni H. , Asfour Abdul‐Fattah A.
Published: March 2009

The pseudo‐binary model developed by Wu and Asfour (1992) has been used to modify some existing viscosity predictive models to that they can predict the viscosities of multicomponent liquid n‐alkane and regular mixtures. The McAllister three‐body interaction model and the Grunberg‐Nissan viscosity equation were both employed, after modification, to successfully predict the viscosity of multicomponent liquid n‐alkane and regular solutions. The modified Generalized Corresponding States Principel (MGCSP) reported by Wu and Asfour (1992), for only predicting the viscosities of n‐alkane mixtures, has been extended to predit the viscosities of multicomponent regular solutions. The predictive capabilities of several predictive models were analyzed. The obtained results showed that the pseudo‐binary McAllister model predicts the viscosity data better than the other existing predictive models.
Estimation of gas hold‐up in aerated vessels
Authors: Paglianti Alessandro , Takenaka Katsuhide , Bujalski Waldemar , Takahashi Koji
Published: March 2009

An attempt to produce a simple equation for gas hold‐up in stirred tank reactors has been made. This new semi‐empirical equation, based on the mass balance for the gas phase, predicts the observed effem due to the tank and impeller diameters and physical properties reasonably well. It can be used both for tanks working with a single Rushton impeller as well as with multiple Rushton impeller systems. The equation has been validated using both data found in literature and from our experiments.
Hydrodynamic behaviour of a magneto airlift column in a transverse magnetic field
Authors: Al‐Qodah Zakaria
Published: March 2009

The hydrodynamics of a three‐phase airlift reactor of magnetic particles has been investigated in the presence of a transverse magnetic field. Experiments were carried out in two modes: applying the magnetic field to a static bed then increasing the field flow, and applying the magnetic field to a fluidized bed then increasing the magnetic field intensity. In magnetizing the first mode and parallel to the increasing gas superficial velocity, several bed regimes were observed, including: initial packed, stabilized, and fluidized beds. On the other hand, in magnetizing last mode and while increasing the magnetic field intensity, the fluidized bed changes from a fluidized to a stabilized to frozen bed. Bed expansion before the onset of fluidization increases as the magnetic field intensity increases. Minimum fluidization velocity was found to be strongly dependent on the magnetic field intensity and the minimum stabilization intensity was also strongly dependent on the gas velocity. The magnetic field intensity also affects the bed expansion hysteresis and the liquid circulation velocity. A photocell was used to measure the water circulation rate in the downcomer of the reactor.
Gas‐liquid mass transfer in low‐ and medium‐consistency pulp suspensions
Authors: Rewatkar V. B. , Bennington C. P. J.
Published: March 2009

The volumetric gas—liquid mass transfer coefficient (kLa) was measured for low‐ and medium‐consistency pulp suspensions using the cobalt‐catalyzed sulfite oxidation technique. Mass transfer rates were measured in a high‐shear mixer for a range of operating parameters, including the rotor speed (N = 10 to 50 rev/s), gas void fraction (Xg = 0.10 to 0.40) and fibre mass concentration (Cm = 0.0 to 0.10). kLa measurements were compared with the macroscale flow regime in the vessel (characterized using photographic techniques) and correlated with energy dissipation, gas void fraction and suspension mass concentration in the mixer. We found that gas‐liquid mass transfer was significantly reduced in pulp suspensions, even for low suspension concentrations. Part of this reduction was associated with dissolved components leached from the fibres into the liquid phase. This could account for reductions in kLa of up to 30% when compared with distilled water. The fibres further reduced kLa, with the magnitude of the decrease depending on the fibre mass concentration. Correlations were developed for kLa and compared with results available in the literature.
Batch kinetics and modelling of propionic acid fermentation
Authors: Goswami Vandana , Srivastava A. K.
Published: March 2009

Batch propionic acid fermentation kinetics was studied using five different initial concentrations of lactose (i.e., 37 g/L, 45g/L, 50g/L, 57 g/L and 73 g/L) at constant temperature (30°C) and pH (6.5) under anaerobic conditions using Propionibacterium acidipropionici (ATCC 4875). When the initial substrate concentration was 37 g/L, 45 g/L, 50 g/L, 57 g/L and 73 g/L, then, correspondingly, 16 g/L, 19 g/L, 22.25 g/L, 25.3 g/L and 26.3 g/L of propionic acid was accumulated in the fermentation broth. Increasing the supply of lactose in the fermentation medium led to the accumulation of by products succinate, acetate and pyruvate. Maximum propionate yield (0.44 g/g) and comparatively lesser impurities (byproducts) were achieved with 57 g/L initial lactose concentration. The batch growth kinetics was eventually used to develop and test a mathematical model for propionic acid fermentation by P. acidipropionici at pH 6.5 and So = 57 g/L. YX/Smax was found to be the most sensitive parameter of the model. The same model also successfully simulated the batch kinetics observed at So = 37 g/L. However the model failed to simulate the fermentation kinetics observed at So = 73 g/L. The developed model can be used for process optimization studies.
Prediction of pressure fluctuations and minimum fluidization velocity of binary mixtures of geldart group b particles in bubbling fluidized beds
Authors: Leu Lii‐Ping , Wu Chih‐Nan
Published: March 2009

A simple method was proposed to find the pressure fluctuations of binary systems of Geldart Group B particles under bubbling fluidized bed conditions. The pressure fluctuations of binary systems could be predicted from the pressure fluctuations of the individual particles component which comprised the binary systems for completely mixed and partially mixed systems. The predicted pressure fluctuations could be used to calculate the minimum fluidization velocity of the binary systems. The predicted and experimental values of pressure fluctuations and the minimum fluidization velocity of binary systems were in fairly good agreement.
Effect of temperature on gas bypassing and solids circulation rate in an internally circulating fluidized bed
Authors: Namkung Won , Guy Christophe , Boisselle Fréadéaric , Legros Robert
Published: March 2009

The effect of bed temperature in the annulus region on gas bypassing from annulus to riser and solids circulation rate has been determined in an internally circulating fluidized bed. The bed voidage in the annulus region increases with increasing temperature. The average fractions of gas bypassing of annulus gas are 59.4% and 87% at room temperature and high temperature (400°C to 800°C), respectively. Solids circulation rate increases with increasing annulus gas velocity, but is nearly independent of riser velocity. Solids circulation rate increases with increasing temperature.
An analysis of the use of electrical power measurements for process control in large‐scale stirred vessels
Authors: Hjorth Sven , Karlsson Lennart , Friberg Paal , Boon Lotte
Published: March 2009

The mechanical power that is transferred to a liquid via the shaft of an agitator is obtained from a measurement of the electrical power flowing into the electric motor within an accuracy of less than 5%. The accuracy obtained is limited by the calibration procedure. As the implementation of an electric power measurement is both simple and comparatively inexpensive, the technique is suitable for a continuous monitoring of the power used by agitators in the process industries.
Dechlorination of 1‐chlorohexadecane and 2‐chloronaphthalene in water under sub‐ and supercritical conditions
Authors: Akimoto Masamichi , Tanaka Hideharu , Watanabe Akiko
Published: March 2009

Reactions of 1‐chlorohexadecane and 2‐chloron‐aphthalene in water under sub‐ and supercritical conditions have been investigated so as to show the possible use of water for the dechlorinations of these organic chlorides. The reactions were carried out at 275°C to 430°C in a small SUS316 batch reactor under nitrogen atmosphere at the molar organic chloride/water ratio of 1/100. Under subcritical temperatures, hydrolysis reactions occurred catalyzed by H+ ions, whereas under supercritical conditions hydrodechlorinations occurred too, in which hydrogens evolved by the reaction of HCI with the metal wall of the reactor participated. The hydrogenation and hydrogenolysis of the primary reaction products also occurred for 1‐chlorohexadecane under supercritical conditions. The dechlorination selectivity was nearly 100% for these organic chlorides irrespective of the reaction conditions employed.