bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress in the kinetics of coal and char gasification
Authors: van Heek Karl Heinrich , Mühlen Heinz‐Jürgen , Jüntgen Harald 
Published: August 2005

AbstractThis contribution reviews the work performed mainly at Bergbau‐Forschung during the past few years. First, it deals with the quantitative description of gasification kinetics, taking into account the pressure of the gasifying agent and partial pressures of product gases. Thereby, a method and quantitative data are provided for the calculation of reaction rates for uncatalyzed and potassium‐catalyzed gasification, on the example of chars from high volatile bituminous coals. In addition, a method for characterization of internal surface area by oxygen chemisorption with respect to char reactivity has been improved. Progress has also been achieved in the assessment of the impact of pyrolysis conditions, especially the time‐temperature profile during char formation, on its chemical activity during subsequent use.
Studies of drop break‐up in liquid‐liquid systems in a rotating disc contactor. Part I: Conditions of no mass transfer
Authors: Bahmanyar Hossein , Slater Michael J. 
Published: August 2005

AbstractObservations on the break‐up of single drops in a rotating disc contactor show that there is a critical rotor speed below which drops of a given size do not break. Weber and Reynolds numbers are required to correlate the data and not simply a Weber number as for turbine agitated systems. The probability of break‐up of a drop at the rotor edge is expressed in terms of a Weber number with a lower limit for critical conditions. The mean number of daughter drops produced on break‐up is correlated as a simple function of drop diameter based on the critical diameter and agreement is found with data from other types of agitated equipment.
Modelling of pressure drop in packed columns
Authors: Billet Reinhard , Schultes Michael 
Published: August 2005

AbstractThe correct choice of packing is of decisive importance for optimum process efficiency in the operation of two‐phase countercurrent columns. An important criterion for this choice is the pressure drop in the gas flow. Theoretical relationships are derived for calculating the pressure drop in beds with dry and trickle packings. It has been demonstrated by comprehensive experiments that these relationships allow the pressure drop to be determined more accurately than by previous methods. The experiments were performed at the Department of Thermal Separation Processes of Bochum University on 54 different packed beds, using 24 different systems.
A new pneumatic bearing dynamometer for power input measurement in stirred tanks
Authors: Reséndiz Roberto , Martínez Alfredo , Ascanio Gabriel , Galindo Enrique 
Published: August 2005

AbstractA turntable dynamometer has been constructed for the accurate measurement of power input and mixing applications in bench stirred tank reactors. The main feature of this device is a pneumatic bearing with complementary conical parts. The conical pneumatic bearing permitted to apply eccentric loads without affecting its stability. The static friction torque in the pneumatic bearing was very small, 4 × 10−4 Nm, and can be neglected in the experimental ranges of measured torques, i.e. from 5 × 10−3 to 2.21 Nm. In accordance with the instrumentation used, the deviations obtained with the apparatus are less than 10% at low torque readings. At moderate torques, deviations lower than 1% are routinely obtained. Several power input measurements show that the obtained data scatter is lower than 2.5%. The power input response in the turbulent regime is in agreement with dimensional analysis: the power input depends on the cube of the impeller speed. In addition, data obtained with a turbine impeller under ungassed conditions agree with the predictions of a published correlation, which takes into account several geometrical parameters.
Development of rate expressions for the catalytic decomposition of nitric oxide with ammonia on iron oxide
Authors: Claußen Michael , Kainer Hartmut , Kunz Ulrich , Hoffmann Ulrich 
Published: August 2005

AbstractThe reduction of nitric oxide with ammonia on iron oxide catalysts has been studied in a continuous‐flow recycle reactor using simulated flue gas in the temperature range from 573 to 673 K. NO and HN3 concentrations were varied between 0 and 1000 vpm, O2 and H2O concentrations between 0 and 9 vol.‐%, the remainder being nitrogen. In the presence of oxygen, the formulated reaction rate equation describes the measured rates of the main reaction NO + 2/3 NH3 ⇄ 5/6 N2 + H2O. Its form corresponds to the Langmuir‐Hinshelwood type. The rate equation well fits the data, which cover the whole industrial temperature and concentration range. In the absence of oxygen, the measured reaction rates can be best described by a power law.
Safe operation of a batch reactor: Safe storage of organic peroxides in supply vessels
Authors: Steensma Metske , Westerterp K. Roel 
Published: August 2005

AbstractIn this study, we investigated the limits of safe operation for a cooled reactor, operated batchwise. As an example of a single‐phase reaction, we studied the decomposition of t‐butyl peroxypivalate, a well‐known organic peroxide, undergoing self‐heating at relatively low temperatures. If sufficiently diluted, it can be supplied to a polymerization process from large, cooled but unstirred vessels. We present a number of extensions to the existing homogeneous explosion theory, namely a practical definition of the critical condition, its calculation, and expressions for the available time before runaway in the case of a supercritical condition, taking into account the effects of natural convection inside the vessel and the reactant conversion. The extensions of the theory were confirmed by adiabatic and non‐adiabatic runaway experiments on bench scale, and natural convection cooling experiments with liquids in various packages.
Hydrodynamics, axial mixing and mass transfer in open turbine rotating disc contactor (OTRDC)
Authors: Jia‐Wen Zhu , Shou‐Hua Zhang , Xiao‐Kui Zhou , Xiao‐Xiang Chen , Yuan‐Fu Su , Vogelpohl Alfons 
Published: August 2005

AbstractAn experimental study of hydrodynamics, axial mixing and mass transfer has been carried out in a newly developed liquid‐liquid extraction contactor, namely the open turbine rotating disc contactor (OTRDC). It has been established that the OTRDC can be operated with larger holdups of the dispersed phase, larger interfaces and, hence, more efficient mass transfer than the conventional RDC. In correlating axial mixing data, a combined model has been applied in which both the forward mixing due to drop size distribution and the backmixing of droplets are taken into account. The RTD curves of dispersed phase predicted by the model agree well with the experimental data. Comparison of experimental mass transfer data with those predicted by the proposed axial mixing model and the theoretical single drop model shows that they are in good agreement.
Modelling of selective catalytic denox reactors – strategy for replacing deactivated catalyst elements
Authors: Lefers Jan B. , Lodder Peter , Enoch Gerd D. 
Published: August 2005

AbstractA simulation model for denox reactors (high dust) containing honeycomb catalysts and operating at temperatures between 300 and 400 °C has been developed. The model predicts the NOx reduction as a function of process variables (temperature, gas velocity, NOx concentration, NH3/NOx ratio) as well as a function of reactor and catalyst geometry (pitch diameter, length of catalyst layer, number of layers). Model parameters such as the rate constant and the adsorption equilibrium constant of NH3 on the catalyst surface were determined by curve fitting of experimental data obtained in a pilot test unit. Based on model calculations, it is shown that the effect of catalyst poisoning (deactivation) on NOx reduction is not the same for every catalyst layer. The lifetimes of catalyst elements located at the inlet to the reactor appear shorter than those of the elements positioned at the outlet from the reactor. Experimental verification of this theoretical finding is required.
Effect of doping with nickel and copper on catalytic behaviour of wide‐pore zeolites with different pore structures
Authors: Exner Herbert , Fetting Fritz 
Published: August 2005

AbstractThe catalytic properties of wide‐pore zeolites, namely Ni‐ and Cu‐doped faujastie H‐Y and H‐mordenite (H‐M) are compared on the example of conversion of n‐hexane. After thermal pretreatment of ion‐exchanged zeolites, reduction with hydrogen (P ≤ 40 bar) leads to a large number of metallic clusters and crystallites as well as ionic species in the zeolites. Notwithstanding this variety, the different types of catalysts can be divided into three classes: classical bifunctional catalysts (for example NiHM, NiHY) with ion exchange degrees > 30%, monofunctional catalysts, such as CuHM and CuHY with high copper contents (ion exchange degree > 40%) and metal‐doped (Ni and Cu) zeolites which, depending on the conditions of pretreatment, act as bifunctional and/or monofunctional compounds and, therefore, show very unstable reaction behaviour. In addition to the extent of reduction, the cation distribution affects the activity and deactivation behaviour and, to a lesser extent, the product selectivity. The reaction mechanism of bifunctional catalysis is similar to that observed in platinum‐doped catalysts, while the mechanism of monofunctional catalysis resembles the process on undoped zeolites.
Infinite‐dilution activity coefficients of organic solutes in methyl phenyl ether, butyl ether and methyl iso‐butyl ketone
Authors: Campanella Enrique A. 
Published: August 2005

AbstractActivity coefficients of hydrocarbons and chloroparaffins at infinite dilution in methyl phenyl ether, butyl ether and methyl iso‐butyl ketone at 293.15 K have been obtained by the retention‐time method in a modified gas chromatograph. The experimental data are compared with predictions of the UNIFAC and MOSCED models. Selectivities for the 1,1,1‐trichloroetane‐1,2‐dichloroetane separation process are reported.
A multi‐parameter model for absorption
Authors: Guha Chandan , Roy Subhash Chandra 
Published: August 2005

AbstractA three‐parameter model for mass transfer by absorption, based on a combined effect of non‐steady‐state molecular and eddy diffusion through a resistance zone has been suggested, which encompasses all the existing theories on mass transfer at the gas‐liquid interface. King's approach [5] to describing gas‐liquid mass transfer phenomena through an eddy‐diffusivity model can explain some experimental results, but does not provide a general mathematical solution of the problem. The shortcomings of the King's model are overcome in the present work and a general solution is presented. This solution confirms the experimental findings of Versteeg et al. [10] for liquid phase mass transfer. The steady‐state solution of the present theory, valid for the dimensionless number α > 0, shows a close agreement with experimental data of Luk [22], the only source of all the information necessary for model verification.
A critical study of multivariable self‐tuning algorithms for distillation control
Authors: Radhakrishnan Thota K. , Gangiah Kota 
Published: August 2005

AbstractA control algorithm which has been acclaimed as the best algorithm for a real system may not be the best algorithm for a different real system. Therefore, various self‐tuning algorithms for real distillation columns have been evaluated, in order to compare their performances. A variable forgetting factor algorithm is modified using a filter which permits the employment of one instead of two covariance matrices for distillation control. A cautious self‐tuning control of SISO system is extended to MIMO system of distillation control. Multivariable self‐tuning regulator, multivariable self‐tuning controller and multivariable cautious self‐tuning controller are implemented with modified variable forgetting factor for linear transfer function model, Waller et al. column, and rigorous non‐linear model, Wood and Berry column. For distillation control, a multivariable cautious self‐tuning algorithm with modified variable forgetting factor is much simpler than earlier reported algorithms. This has produced better results and demonstrated its effectiveness, even in the presence of noise when other adaptive controllers give unsatisfactory performance.
Dynamic modelling of multitubular catalytic reactors
Authors: Stankiewicz Andrzej , Eigenberger G. Gerhart 
Published: August 2005

AbstractThis paper presents a study on modelling and simulation of transient operational characteristics in multitubular fixed‐bed reactors. The dynamic model of the reactor is based on a “porous body” approach which regards the intertubular space as a pseudo‐homogeneous environment. Such an approach permits to take into account most factors in the geometrical design of the unit and thus to study the influence of various shell‐side geometrical and operational parameters on the reactor behaviour. Based on the model, the dynamic responses of the two most common industrial reactor designs, i.e. the parallel flow unit with distributing plates and the crossflow reactor with disk‐and‐doughnut baffles have been investigated and compared. In addition, some problems of correct space discretization and use of time‐dependent regridding procedures, are discussed.
A learning fedforward control strategy for the concentration control of recycle reactors. Part I: Set‐point control
Authors: Schnitzlein Klaus , Löwe Arno 
Published: August 2005

AbstractUnknown reaction rates make concentration control in laboratory recycle reactors a difficult task, particularly when gas chromatographs or other analytical equipment with long analysis times from part of the control system. For such time‐delay systems, a model‐based feedforward control technique is developed which uses some kind of learning linear mapping to provide estimates of the reaction rates. Regarding the number of time steps necessary to satisfy a new set point, in a variety of simulation studies, this technique has proven superior to similar but simpler control strategies.
Investigation on pure shearing of cohesive limestone with true biaxial shear tester
Authors: Nowak Marek , Schwedes Jörg 
Published: August 2005

AbstractPure shear deformation of a bulk solid sample was performed with the True Biaxial Shear Tester. The influence of stress history on pure shearing was examined by three different consolidation procedures. Apart from the influence of the consolidation procedure, the effect of volume change, i.e. the change in the bulk solid density during consolidation, on pure shear deformation was investigated. Cohesive limestone with x50 = 5 μm was used for the experiments.
Mixing times in stirred suspensions
Authors: Kraume Matthias 
Published: August 2005

AbstractIn stirred systems, the presence of solid particles leads to a pronounced lengthening of mixing time, sometimes to over 10 times that for the single‐phase state. The mixing behaviour is strongly heterogeneous, since the slurry is mixed comparatively rapidly, while markedly slower homogenization occurs in the solid‐free zone. This is the consequence of different fluid velocities in the two regions. For particle settling velocities in excess of 5 cm/s, mixing times assume maximum values on reaching the state of complete suspension. By contrast, at lower settling velocities, maximum mixing times occur before suspension is complete. Mixing times are influenced only be the state of suspension and not by the mode of its generation. Consequently, for the fulfilment of the 90% suspended slurry height criterion, mixing times are independent of stirrer speed, solid concentration, type of agitator or diameter ratio d/D. The effects of particle diameter, viscosity and equipment dimensions on mixing time, when the 90% slurry height criterion is fulfilled, are reflected by the ratio of the vessel diameter to a representative liquid velocity.
Significance of axial heat dispersion for the description of heat transport in wall‐cooled packed beds
Authors: Borkink J. G. Harold , Westerterp K. Roel 
Published: August 2005

AbstractA two‐dimensional pseudo‐homogeneous model with axial dispersion of heat has been solved numerically with different boundary conditions at the inlet and outlet of the packed bed. The model solutions are fitted to experimental temperature profiles, determined in a wall‐cooled packed bed in which a hot gas is cooled down, and best fit values of the effective axial and radial thermal conductivities and the wall heat transfer coefficient are obtained. In the range of Reynolds numbers employed, Re > 50, the axial dispersion of heat is found to be of no significance for the description of heat transport in wall‐cooled packed beds without reaction, provided that the inlet boundary conditions are chosen appropriately. If a radially flat inlet temperature profile is assumed, while the actual profile is curved, an apparent improvement in the description of heat transport is observed when axial dispersion is incorporated into the heat balance and high effective axial thermal conductivities are obtained. If a Danckwerts type inlet boundary condition is used, assuming a flat temperature profile immediately in front of the inlet, an apparent improvement is also found on incorporation of axial dispersion of heat. This is caused by the temperature jump at the inlet, compensating for the overestimation of inlet temperature, in the case of cooling. The latter also explains why the inclusion of axial dispersion may eliminate the so‐called “length effect”, often related to the effective radial thermal conductivity and the wall heat transfer coefficient. It is shown for the outlet boundary condition that deletion of the axial dispersion term from the heat balance at the outlet is a convenient boundary condition for the model being solved numerically.
Electrical conductivities of pure organic liquids
Authors: Horvath Ari L. 
Published: August 2005

AbstractThis contribution presents a method of evaluating electrical conductivities of pure organic liquids. Emphasis is placed on the methodology of selection, correlation and analysis of experimental data. The proposed method brings order out of conflicting, confusing and chaotic experimental observations. It is also shown that the consistent and evaluated data are generated at a fraction of the cost and time required for producing the original raw experimental data.
Micromixing effects on a parallel reaction in flow reactors
Authors: Atiqullah Muhammad , Hassan Mirza M. , Beg Shafkat A. 
Published: August 2005

AbstractUsing the micromixing concepts of Danckwerts and Zwietering, the Peclet number Pe has been correlated mathematically to the degree of segregation J for the axial dispersion model. The results were applied to compare the micromixing effects on a model, mixed‐order parallel reaction system in continuous flow reactors. Axial dispersion model, and Ng and Rippin's two‐environment model were used to find the micromixing effects in tubular and stirred tank reactors, respectively. The performance of these reactors, with varying geometries, has been evaluated in terms of overall conversion, selectivity, and yield under identical operating and reaction conditions. The overall conversion increases in a tubular reactor with the increase in J, irrespective of the kinetic orders. However, in a stirred tank reactor, the conversion is found to be micromixing‐sensitive, depending on the order of reaction. For m = 1 and n = 2 (case 1), the conversion is fairly insensitive to micromixing effects while it decreases for m = 0.5 and n = 1 (case 2) with increasing J. For the same extent of micromixing, a tubular reactor gives, in both cases, a higher conversion than a stirred tank reactor. The selectivity, in either case, decreases in both reactors with increasing segregation effects. However, in each case, the selectivity of a tubular reactor was fairly close to that of a stirred tank reactor at the same value of J. As far as the yield is concerned, both reactors achieve nearly the same value, without significant micromixing effects.
Drying characteristics of starch in an inert medium fluidized bed
Authors: Lee Dong‐Hyun , Kim Sang‐Done 
Published: August 2005

AbstractThe effects of gas velocity (0.32 to 0.67 m/s), inlet gas temperature (25 to 100 °C) and the mass ratio of starch to inert particles (0.1 to 0.4) on the drying rate of starch in a 0.083 m‐ID × 0.80 m‐high inert medium fluidized bed were investigated. The drying mechanism in an inert medium fluidized bed can be classified into adhesion‐dispersion, evaporation and disintegration steps. The drying rate increases with the increasing inlet gas temperature and velocity; the rates being about 10 times those reported for an agitated pan dryer. However, the drying rate decreases slightly as the mass ratio of starch to inert particles increases. Also, the drying rate exhibits a maximum at an optimum bed porosity. The drying rate data obtained in an inert medium fluidized bed have been correlated with the relevant dimensionless groups, i.e. Stefan and particle Reynolds numbers based on the theory of isotropic turbulence.
Techno‐Economic investigation of an air humidification‐dehumidification desalination process
Authors: Khedr Maaly 
Published: August 2005

AbstractThis article presents a humidification‐dehumidification (H.D.) process suitable for desalination of sea‐ and brackish water. The work correlates performance characteristics of the combination of different components in such a loop. Water yield, energy requirement and design data are evaluated as functions of different parameters. The investigation covered water to air mass ratios ranging from 60 to 80, concentration ratios between 2 and 5, at a temperature difference of between 10 and 16 °C, along the liquid for dehumidification. The results showed that 76% of energy consumed in the humidifier is recovered by condensation. Increase of the concentration ratio to 5 can reduce the make‐up water and rejected brine by about 58% and 24% respectively. Cost calculations show that the H.D. process has significant potential as an alternative for small capacity desalination plants and permits to operate systems as small as 10 m3/day in output.
Cooling water treatment by ozonization
Authors: Lin Sheng H. , Yeh Kuo L. 
Published: August 2005

AbstractOzonization of water in a cooling tower was investigated. A laboratory experimental set‐up was employed to study changes in water quality during ozonization. Measured data were analyzed in the context of cooling water's resistance to corrosion, scaling and biofouling. A method is proposed for determining the suitable dosage of ozone for maintaining the necessary water quality. It has been found that ozonization is very effective in maintaining the correct water quality for the required purpose and provides an attractive alternative to the conventional multiple chemical method of cooling water treatment.