bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of shallow fluidized bed reactors: II. Analytical and numerical solutions
Authors: Chang C. C. , Rong S. X. , Fan L. T. 
Published: March 2009

AbstractA general dynamic model derived previously for shallow fluidized bed reactors with continuous solids flow has been extended. The model includes explicitly the convective and dispersive flows of solids in the lateral direction of the bed. The performance of the fluidized bed zinc sulfide roaster is simulated by solving the resultant dynamic governing equations. Steady‐state analytical solutions are obtained after simplifications of governing equations. The numerically obtained transient solutions approach these analytical solutions as time increases. A series of computations has been carried out to examine the effects of significant parameters, including the bubble size, Peclet number, crossflow ratio, Dämkohler number and superficial velocity of the fluidizing gas, on the performance of the shallow fluidized bed reactor.
Wood liquefaction: Extended batch reactions using raney nickel catalyst
Authors: Boocock D. G. B. , Mackay D. , Lee P. 
Published: March 2009

AbstractExtended batch reactions, in which poplar is treated at 340°C in the presence of Raney nickel, water and hydrogen, give oil in yields of 36‐41% with oxygen contents of 12‐17%. Methane and carbon dioxide formation, hydrogen utilisation and cracking of the oil are favoured by fresh Raney nickel. There is some competition for methane and carbon dioxide production, higher hydrogen pressures favouring the former in the presence of fresh catalyst. Efficient mass transfer increases hydrogen utilisation and lowers the oil viscosity. It is concluded that Raney nickel has no significant advantage over other more convenient forms of nickel.
Liquefaction of coal by SRC‐II process: Part V: Dynamic thermal behavior of the reactor
Authors: Singh Chandra P. P. , Carr Norman L. 
Published: March 2009

AbstractCriteria for identification of the unstable or stable nature of the steady state based on the reactor temperature response to step changes in feed temperature, and a dynamic thermal simulation of SRC‐II reactors are developed. These are used in the analysis of a dynamic SRC‐II reactor experiment to confirm its unstable operation under normal process conditions. The simulation is used further to study the sensitivity of reactor temperature to changes in feed temperature and to variations in the total heat capacity of the reactor vessel and insulation materials. It is shown that, under normal SRC‐II process conditions, it would take about an hour for the reactor temperature to change by ± 10°C, if no controls were used. With quench gas manipulation, the reactor temperature could be maintained within ± 1°C even for a sustained small perturbation in the process conditions. Therefore, in spite of its unstable character, the SRC‐II reactors can be readily operated with quench gas manipulation without incurring any major temperature control problems.
Some aspects of liquid‐solid fluidized beds
Authors: Rao K. V. K. , Prakash S. G. 
Published: March 2009

AbstractHydrodynamic characteristics of randomly packed fluidized beds were investigated using particles of different sizes and densities fluidized with water.The minimum fluidization velocity was found to be independent of the initial bed height. The minimum fluidization velocity was found to be

Bed expansion followed the Richardson Zaki relationship and the exponent 'n' has been correlated as:
The uranium fuel cycle: Some aspects of the physics, chemistry and measurement of radon and thoron daughters
Authors: Phillips Colin R. 
Published: March 2009

AbstractMuch effort has been devoted world‐wide towards minimizing exposure to radon and thoron daughters in the exploitation of nuclear energy. In this work, the behaviour of radon and thoron daughters after formation from their gas precursors is discussed, together with optimally designed measurement and dosimetry methods for assessing alpha radiation exposure in uranium mines and mills, in buildings and in the environment. The interaction of radon and thoron daughters with aerosol particles, which is very important in determining the fate of the airborne radioactivity, can be described better in terms of activity‐size distributions than by use of the commonly applied concepts of “attached” and “unattached” fractions. Further, the properties of the aerosol‐daughter system are shown to depend upon humidity and the presence of trace gases, which serve as electron sources to neutralize the newly‐formed positive daughters. Finally, the mechanisms of release of radium and radon from ore and soil are discussed. The significance of the various conclusions to practical situations is emphasized.
Characterization of chemisorbed species in CO/H2 and CO2/H2 reactions. Evolutive behaviour of the species
Authors: Hindermann J. P. , Deluzarche A. , Kieffer R. , Kiennemann A. 
Published: March 2009

AbstractBy applying the chemical trapping method to the hydrocondensation reaction of carbon monoxide, we propose a reaction scheme with some novel interesting features. In the chemisorption of CO on Ni/SiO2, Ni/Al2 O3, Co, Co/Al2 O3 we detected species bonded both through the C and O ends of the molecule. This chemisorbed CO can be the intermediate of the dissociation of CO or lead to the formation of a formyl species by reaction with hydrogen. The competition of these two reactions can lead to hydrocarbons or to alcohols.
The higher alcohol synthesis over promoted Cu/ZnO catalysts
Authors: Smith Kevin J. , Anderson Robert B. 
Published: March 2009

AbstractAlkali oxides added to methanol catalysts increase the formation of ethanol, n‐propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper‐zinc oxide catalyst promoted with K2 CO3 are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H2 to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied as p p while for methanol, ethanol and n‐propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameters are given.
RTD for diffusion‐free laminar flow of non‐newtonian fluids through coiled tubes
Authors: Saxena A. K. , Nigam K. M. , Nigam K. D. P. 
Published: March 2009

AbstractThe residence time distribution (RTD) for diffusion‐free laminar helical flow of non‐Newtonian fluids has been numerically computed for values of the power‐law index from 0.2 to 2.0. Experimental verification is also provided. Excellent agreement is also shown with independently calculated RTD's appearing in the literature.
Oxygen mass transfer in three‐phase fluidized beds working at large flow rates
Authors: Alvarez‐Cuenca M. , Baker C. G. J. , Bergougnou M. A. , Nerenberg M. A. 
Published: March 2009

AbstractThe published literature on gas mass transfer in three‐phase fluidized beds indicates that most of the research done in the last two decades has been carried out at low superficial velocities and/or volumetric flow rates. These experimental limitations are reflected in the current understanding of these systems. In this investigation, performed at large gas and liquid velocities and flow rates, the behaviour of three‐phase fluidized beds of 0.1, 0.3 and 0.5 cm diameter glass beads has been studied.Computer‐made contour diagrams, obtained from the mapping of the oxygen concentration in the column have proven to be an effective probing technique. These diagrams permit the description of flow patterns and bed hydrodynamic properties otherwise not observable with tracers.The use of concentration and pressure profiles complements the observations made with the contour diagrams. At low gas and liquid velocities the concentration profiles are S‐shaped. As Vgand Vlincrease the three absorption zones, observed in those S‐shaped profiles, become two zone similar to those observed in bubble columns. The interface between the dense bed and dilute phase is characterized by an unusually high mass transfer activity.
Bitumen hydroprocessing: Effects of metal loading and promoters in Mo‐Al2 O3 catalytic systems
Authors: Kriz J. F. 
Published: March 2009

AbstractAthabasca bitumen and a heavy gas oil (345−525°C) derived from it were used in a high‐pressure continuous‐flow system to evaluate catalytic effects of metal loading in hydroprocessing and to assess the role of promoters represented here by cobalt and sodium. A method that can be used for analysis of these effects is suggested. The two feedstocks are compared in view of the expected catalyst performance and requirements in each case. It was found that desirable effects of promoters were greatest at low temperatures and with catalysts having low total metal loading. Desirable effects of catalysts having high molybdenum loading were intensified with increasing temperatures. These trends were similar with both feedstocks but the effects were much less pronounced with bitumen than with the gas oil. The need for an effective hydrogenation component was identified.
A quantitative theoretical treatment of the fischer tropsch synthesis
Authors: Taylor P. D. , Wojciechowski B. W. 
Published: March 2009

AbstractA generalized scheme for product distribution in Fischer Tropsch synthesis in the absence of non‐kinetic effects due to diffusion, shape selectivity, catalyst bifunctionality (e.g. synthesis‐cracking catalysts), etc. is presented. The derivations reproduce the Schulz‐Flory distribution in one limit and go on to generalize the work of Anderson in predicting the distribution of methylated species in the synthesis product. Formulae for molar distributions, weight distributions and weight distribution modes are presented. It is shown that special cases of the generalized distributions lead to methanol production or methanation as well as predicting other, as yet unreported, product compositions.
A general criterion to test the relative importance of intraparticle and external heat and mass transfer resistances in porous catalysts
Authors: Doǧu Timur 
Published: March 2009

AbstractA general criterion is developed for testing the relative importance of intraparticle and external, concentration and temperature gradients on the observed rates, for reactions catalyzed by porous solids. The criterion is applicable to any multiple reaction system and to reactions conforming to any rate law. The applicability of such criteria is extended to reaction systems with highly nonlinear temperature and concentration dependence, by taking into‐account the higher order terms in the Taylor expansion of the rate expressions in the derivation.
Comparisons of the yields and properties of the oil products from direct thermochemical biomass liquefaction processes
Authors: Beckman David , Elliott Douglas C. 
Published: March 2009

AbstractSeveral different direct thermochemical biomass conversion processes are compared based on the results of an experimental program using standard wood and peat feedstocks. The program was part of the International Energy Agency, Biomass Liquefaction Test Facility project. The operating conditions of the processes compared differed greatly. General correlations of the properties of the oils produced from these processes are made based on the severity of the operating conditions. Important parameters in considering process severity are temperature, pressure, time at reaction conditions and added reactants or catalysts.
Multistage continuous cultivation of blue‐green alga spirulina maxima in the flat tank photobioreactors with recycle
Authors: Samson Réjean , Leduy Anh 
Published: March 2009

AbstractSpirulina maxima was continuously cultivated in four 64‐liter flat tank photobioreactors in cascade, under continuous 30 klx fluorescent light and nonaseptic condition, in an industrial grade synthetic medium which bubbled with atmospheric air. The increase in the number of stages resulted in the higher biomass concentration and allowed operation with a dilution rate D higher than the alga specific growth rate μ. However, multistage operation does not permit a significant increase in productivity. The recycling of the all culture medium with biomass increased the net productivity of the first two stages of the multistage system. The flat tank design offered great advantages over other geometrical configurations by occupying less space for indoor cultivation, minimizing the water loss by evaporation, and permitting a greater flexibility in construction, installation, and operation. This system was operating continuously for two years in our laboratory for indoor mass production of S. maxima biomass. The flat tank configuration gave the highest areal productivity Pa = 60.5 g/m2·d and highest volumetric productivity Pv = 1.17 g/L·d when operated as a single stage continuous cultivation with high solid recycle. These values are the highest ever reported for any indoor or outdoor mass production system for S. maxima.
Comparison of primal and dual solution methods for the chemical equilibrium problem using GRG and sensitivity analysis
Authors: Ruda M. M. , Thompson D. W. 
Published: March 2009

AbstractThe calculation of the composition of a reacting mixture when it reaches equilibrium can be regarded as a dual Geometric Program; there is a related primal Geometric Program with fewer variables than the dual. Both primal and dual formulations were compared using the Generalized Reduced Gradient (GRG) algorithm for systems containing 8, 10 and 24 reacting species. The primal proved to be faster (30%) than the dual, and more robust.A sensitivity analysis method suggested by Rijckaert (1974) was tested and the results were compared with re‐solving the original problem. Sensitivity analysis was faster than re‐optimization (50%) but the accuracy of the results depended strongly on the particular problem.
Equilibria of H2S and CO2 in triethanolamine solutions
Authors: Jou F.‐Y. , Otto F. D. , Mather A. E. 
Published: March 2009

AbstractThe equilibrium solubility of H2S and CO2 has been measured in 2.0, 3.5 and 5.0 mol/L triethanolamine solutions. Data were obtained at temperatures of 25°, 50°, 75°, 100° and 125°C at partial pressures of the acid gases ranging from 0.01 to 6360 kPa. Enthalpies of solution were calculated from the solubility data.
The equilibrium phase properties of selected mesitylene binary systems: Mesitylene—methane and mesitylene—carbon dioxide
Authors: Huang Sam. S.‐S. , Robinson Donald B. 
Published: March 2009

AbstractVapor and liquid equilibrium phase compositions have been determined at 310.9, 394.3, and 477.6 K for the mesitylene–methane binary system and at 310.9, 338.7, 394.3, and 477.6 K for the mesitylene–carbon dioxide system. At each temperature, the pressure ranged from the vapor pressure of mesitylene to about 15 MPa, although in the case of the mesitylene–carbon dioxide system, pressures were extended to the vicinity of the critical region at about 18 MPa. The data were used to calculate equilibrium ratios for each component in the binary system.
Coal gasification condensate water: Thermodynamic modeling of gas quench effluent
Authors: Mcaskill R. D. , Bhattacharyya D. , Kermode R. I. 
Published: March 2009

AbstractThe partial oxidation products from a coal gasification process may contain substantial quantities of tars, phenols, ammonia, H2S, CO, CO2, H2, and water vapor. Cooling below the dew point produces condensate water which must be treated before it can be reused or discharged into the environment.A rigorous computer model based on equilibrium thermodynamics has been developed to predict gas and condensate composition for one or more quench steps. Recycle as well as addition of fresh water to one or more stages has been included. Condensate quantities and composition as a function of quenching temperature are calculated for three gasification conditions. A flow diagram for multi‐stage effluent treatment before reuse or discharge is proposed.
Investigation of a fixed‐bed pilot plant reactor by dynamic experimentation. Part 1. Apparatus and experimental results
Authors: Baiker Alfons , Bergougnan Michel 
Published: March 2009

AbstractA non‐isothermal, non‐adiabatic fixed‐bed pilot reactor specially designed for fast measurement of axial and radial temperature and concentration profiles during dynamic experiments is described. The pilot plant is interfaced to a process computer and facilitates conducting different types of dynamic experiments, such as those with simultaneous un‐correlated periodic changes of the process variables. This type of dynamic experiments proved to be most efficient for collecting the data necessary for reactor modelling. Axial and radial temperature and concentration profiles in the fixed bed were measured during catalytic hydrogenation of toluene on an industrial nickel catalyst. Peak shaped perturbations were employed to study the parametric sensitivity of the reactor behaviour and to estimate the reaction kinetics.
Investigation to develop methods for removal of oxygen from coals
Authors: Cooke N. E. , Khandhadia P. S. , Furimsky E. 
Published: March 2009

AbstractSeveral inorganic reducing agents of various chemical characteristics have been tested to see if they reduce the oxygen contained in coal. It was found that oxygen content of coals decreased when they were heated in only water (blank runs). The treatment with the reducing agents containing sulphur did not increase the oxygen removal over that achieved in the blank runs. However, it appears that the ferrous salt catalytically deoxygenated both the lignite and bituminous coals.
Effectiveness factor under cyclic operation of a reactor
Authors: Jain A. K. , Hudgins R. R. , Silveston P. L. 
Published: March 2009

AbstractResults are reported on the influence of intraparticle diffusion on the measured rate of reaction under a condition where the feed composition is changing periodically. The specific application is to cyclic operation of an ammonia synthesis reactor.The effectiveness factor calculated relative to the steady‐state kinetic rates for the time‐average feed condition for fine particles was higher than the comparable steady‐state effectiveness factor as a result of the rate improvement due to cycling.The effectiveness factor calculated relative to the time‐average rate of reaction under cyclic operation for the fine particles was much less than unity and similar numerically to the steady‐state effectiveness factor. The cycling effectiveness factor by either definition varied with cycling conditions because of the complex interaction of cycling parameters.
The effect of liquid viscosity on gas holdup in a vertical pipe
Authors: Weiss R. G. , Foster N. R. , Clark K. N. 
Published: March 2009

AbstractThe effect of liquid viscosity on gas holdup in a 15.1 mm diameter vertical pipe was assessed over the viscosity range 0.00092‐1.670 N s m‐2. Gas holdup increased with increased liquid viscosity. The sensitivity of holdup to changes in viscosity was slight at low viscosity but was markedly increased at higher viscosities.Gas holdup was found to be well described, over the viscosity range studied, by the empirical equation:
Turbulence model predictions of the radial jet — A comparison of κ‐ϵ models
Authors: Wood P. E. , Chen C. P. 
Published: March 2009

AbstractThe (κ‐ϵ) turbulence closure model has become a widely used means of predicting turbulent fluid flows. In this paper the turbulent radial jet, the round jet and the plane jet are calculated in their similarity regions using various versions of the (κ‐ϵ) model to determine which is the most satisfactory for both plane and axisymmetric flows. The most general predictions were obtained using a model which contained additional terms to account for the effect of irrotational strains on the production of turbulence energy. Additionally, detailed mean velocity profiles and turbulence kinetic energy profiles of the radial jet are compared to the available experimental data.
Characteristics of Taylor vortex structure in combined axial and rotating flow
Authors: Gu Z. H. , Fahidy T. Z. 
Published: March 2009

AbstractThe sequential form of the axial displacement of inclined Taylor vortices and their progressive degeneration to horizontal streaks due to the increasing dominance of axial flow is demonstrated via an analytical indicator‐based direct flow visualization technique applied to a concentric cylinder cell with the inner cylinder rotating.
Experimental investigation of low reynolds number flows of liquid‐liquid jets
Authors: Koob E. L. , Hill G. A. 
Published: March 2009

AbstractThe shapes of liquid jets issuing from tubes into a second immiscible liquid are examined experimentally. Previous theoretical work is seen to be based on boundary layer theory and therefore not applicable to low Reynolds number jets as presented here. However, these works have provided insight into dimensionless parameters which could be important in governing this process. The experimental data is presented in the form of these dimensionless groups so that their significance can be explored.The results clearly show that the dispersed phase Reynolds number and the viscosity ratio of the two liquid jets are the most important parameters affecting jet shape. Non‐Newtonian elasticity is seen to contribute to jet expansion but not as much as in the case of inviscid jet swelling. The continuous phase is seen to have a component of velocity far from the jet surface unlike the assumption used in boundary layer theory.The boundary layer theory of Schlichting was extended to predict jet shapes for a viscosity ratio of one. It is seen that the theory does not apply within 15 dimensionless distances from the tube exit. Accurate predictions will require more precise evaluation of the equations of motion.
Local droplet diameter variation in a stirred tank
Authors: Tanaka Masato 
Published: March 2009

AbstractThe local variation of droplet diameter in a stirred tank was measured in the vicinity of the impeller and at another region. The degree of difference in droplet diameter between regions increases with the impeller speed.A correlation equation between the local difference in droplet diameter and the frequencies of coalescence and circulation of the droplet was derived according to the circulation interaction model. The degree of local difference in droplet diameter was found to be controlled strongly by the ratio of coalescence to circulation frequency.
Prediction of pressure drop and void‐fraction in annular two‐phase flows
Authors: Kadambi V. 
Published: March 2009

AbstractThe polynomial vvelocity profile due to Pai (1953), applicable to transition and turbulent conditions in single phase flow, has been used to solve the equations of two‐phase annular flow with appropriate matching conditions at the interface and at the boundaries. The results obtained enable one to predict the pressure drop and the void‐fraction, when the interfacial friction factor is specified. Entrainment of the liquid in the core of the flowing gas has been taken into account by using the empirical relation of Hutchinson and Whalley (1973). It has been shown that the theory provides results in agreement with horizontal tube and vertical tube adiabatic flow data, in addition to predicting the liquid film thickness accurately.