bluuebunny/crossref_metadata_2025 huggingface dataset:
The contradiction in the theory of desorption phenomena: A new interpretation of the classical concept for its avoidance
Authors: Kasai Takeshi
Published: August 2005

Most chemical engineers presently accept that the mass transfer rate in desorption from the solid to the gas phase or from the liquid to the gas phase is accelerated with increasing temperature in the liquid or the solid phase, or increasing partial pressure of inert gas in the gas phase, and/or decreasing total system pressure in the gas phase. Nevertheless, many reports about such mass transfer are still based on the former concept, which completely contradicts the actual phenomena mentioned above. Here, we discuss the contradiction and suggest a way of resolving it in terms of diffusion theory.
Influence of turbulence on transient premixed flame propagation inside closed vessels
Authors: Leuckel Wolfgang , Nastoll Willi , Zarzalis Nikolas
Published: August 2005

The explosion behaviour of CH4/air mixtures inside a closed 0.065 m3 spherical and a 1 m3 cylindrical vessel was investigated to determine the effect of turbulence on the structure and propagation rate of transient turbulent flames for different initial turbulence levels generated by 4 ventilators installed inside the equipment. Laser‐Doppler and hot wire anemometry were used to measure the turbulent motion. It was found that fairly uniform turbulence could be achieved in the central zones of the vessels and that the RMS‐values of flow velocity were proportional to the ventilator speed. The evaluation of burning velocity from the pressure/time records showed that, starting from an initial burning velocity which depends on the initial turbulence level, the flame accelerates as a result of pressure, temperature and turbulence effects. Maximum burning velocity coincides with the inflexion point of the pressure/time curve, and is followed by a rapid deceleration of the flame front. A linear relationship between burning velocity and measured RMS‐velocity is recognized in the observed range of RMS‐values.
Heat and mass transfer during condensation of steam in the presence of air at pressures of up to 21 bar
Authors: Numrich Reiner , Rennhack Rolf
Published: August 2005

Film theory under consideration of one‐sided diffusion is a satisfactory basis for the calculation of vapour condensation from a flowing turbulent mixture with non‐condensable gases. At atmospheric pressure and low condensate flow rates, coefficient equations for smooth tubes are used as a rule. At higher pressures and thus, at higher temperatures and gas densities, there are additional parameters. For instance, non‐ideal behaviour of the gas phase or the surface roughness affects the condensation process. These parameters were examined in a test plant under variation of pressure, steam concentration and temperature in a vapour/air mixture. At pressures of up to 21 bar, the Reynolds number of the gaseous phase reaches a maximum value of 128 000 and of 720 for the condensed phase. After description of the test facility, the experimental results are explained and discussed. It is shown that the experimental results are not in a good agreement with the common calculating methods. Taking into account the non‐ideal behaviour of the steam/air mixture and the roughness of condensate surface by using a friction factor ξr, all the results could be calculated with an accuracy of ± 20%. This was achived with a modification of the coefficient equation of Gnielinski [1] and by using the equation of Andreussi [2] for the friction factor of a cocurrent annular flow. With respect to one‐sided diffusion, the film theory is still applicable. The described method for the determination of local transfer coefficients includes the common calculating method. It represents an extension of the general validity of the film theory.
Study of mass transfer in a centrifugal film apparatus
Authors: Uchida Shigeo , Kamo Hiroshi , Itoh Eiji , Kybota Atsushi , Kawai Sumio
Published: August 2005

Mass transfer data are presented for absorption of oxygen in a centrifugal film apparatus. The apparatus was designed to exclude the formation of foam by gas dispersion in liquid. Cells and micro‐organisms are not subjected to high shear stress. Therefore, this equipment can be applied in fermentation processes. In the present work, experimental data and correlations were obtained on splitting of the liquid film and oxygen absorption into the film through a spiral ridge formed on the conical surface. The performance of the apparatus is found to be equivalent to those of other types of absorbers.
Characterization of mixing and residence time distributions in nozzle‐type reactors
Authors: Coker Akintunde Kayode , Jeffreys Geoffrey Vaughan , Mumford Clive James
Published: August 2005

Studies of flow characteristics and residence time distribution, (RTD), have been undertaken in a range of geometrically similar, laboratory nozzle‐type reactors. High‐speed cine‐photography was employed to record the complex phenomena of liquid mixing in the reactor and also to record on film the colour of an injected tracer solution leaving in the effluent. A novel atomic absorption spectrophotometric (AAS) technique was applied to transform the results of the latter film into response curves. This technique provide detailed quantitative data on the residence time distributions (RTD) for different feed rates. A multiparameter model, comprising a network of CSTR's and plug flows, was developed to simulate the experimental response data. Good agreement was obtained between model predictions and experimental results. The experimental technique and theoretical approach are recommended for analyzing the flow patterns and mixing mechanisms in such reactors.
Particle collection in small laboratory cyclones as a basis for the design of large‐scale cyclones
Authors: Büttner Helmut , Ebert Fritz
Published: August 2005

Grade efficiencies must be measured in order to characterize particle collection in cyclones. For real, irregularly shaped partcles, the grade efficiencies depend on the shape and orientation of the particles and the flow around them. Therefore, the collection characteristics of cyclones should be defined in relation to spherical particles. Deviations occurring on the use of real, irregularly shaped dusts can then be attributed to a material influence. A fast and accurate measuring technique to determine the collection characteristic for spherical particles is described, followed by the presentation of results of extensive investigations on small model cyclones. A similarity relationship is presented. The validity of this relationship was confirmed by investigations with similar, larger cyclones.
Heat transfer to liquids and suspensions in agitated narrow vessels
Authors: Frobese Dirk‐Hans , Bohnet Matthias
Published: August 2005

The knowledge of the heat transfer coefficient on the inner side of a heated vessel wall is of the utmost importance for the design of agitated vessels. In the case of large Reynolds numbers, the heat transfer is mainly determined by these numbers whereas, with small Reynolds numbers, the heat transfer is better described by considering the Grashof number. Investigations of heat transfer in agitated narrow vessels have shown that the height/diameter ratio exerts virtually no influence on the heat transfer when multi‐impeller stirrers are used. The heat transfer to stirred suspensions can be described by relationships valid for liquids if the characteristic data of the liquid are replaced by those of the suspension and when the solids volume concentration is also taken into account. This relationship allows the heat transfer coefficient to be calculated for given solids volume concentrations of up to 60%.
Design and analysis of a state observer for the temperature front of a retification column
Authors: Wozny Günter , Fieg Georg , Jeromin Lutz , Köhne Manfred , Gülich Horst
Published: August 2005

In order to achieve optimal energy‐saving, load‐dependent operation of rectification columns, development and implementation of model‐based control concepts are necessary. This paper reports on the design and step‐by‐step testing of a state observer for the estimation of two state variables which cannot be measured directly, namely the vapour rate and the location of mass transfer zone (temperature front) in the stripping section of a production column. The procedure is described, and the relevant simulation and operation results are presented and discussed. Initial experience, gained when the concept was put into practical operation, is reported.
Experienmental and theoretical combustion rates of graphite plates in hot parallel flows of air and O2/N2 mixtures
Authors: Wilhelmi Herbert , Waibel Rudi , Lippig Volker , Straub Dieter
Published: August 2005

Combustion rate of flat graphite plates in oxidizing flows with velocities of up to 80 m/s and stagnation temperatures between 1600 and 2500 K were investigated. The flow field and its local properties were recorded in addition to surface temperature of the solid sample and change in surface structure. The experiments, in which the surface temperature of graphite was adjusted and carefully controlled by radiation shields, indicated that, under these experimental conditions, between 15 and 20 wt‐% of carbon was lost as particles of up to 100 μm which burnt rapidly in the boundary layer region. Subtraction of erosion rates from the recorded global combustion rates yield the heterogeneous chemical reaction rates, which are approximated by an Arrhenius type function for the mathematical modelling. Since steep temperature and concentration gradients occur in the boundary layer, the local values of the multicomponent transport coefficients were evaluated in order to design a more realistic computational procedure which, in addition, also includes radiative heat transfer. Computational checks revealed that, in the past, the assumption of mean constant values for the transport coefficients has led to errors of up to 100% in the evaluation of the chemical reaction and global combustion rates.
Simulation of primary and secondary reformers for improved energy performance of an ammonia plant
Authors: Ravi K. , Dhingra Subhash Chander , Guha Barun Kumar , Joshi Yogesh Kumar
Published: August 2005

The energy consumption of ammonia plants based on steam reforming of naphtha or natural gas can be reduced by shifting the reforming load from the primary to the secondary reformer. It is shown that lowering of the primary reformer operating temperature 20 °C results in 2% increase of unconverted methane content in the outlet stream. The increased methane content can be processed in the secondary reformer if the process air inlet temperature is increased to 400 °C. The lower operating temperature reduces the energy consumption of the primary reformer by about 6% (and the overall consumption by about 2%) and also prolongs the service life of reformer tubes.
Overproduction of lipase with staphylococcus carnosus (pLipPS1) under modified gravity in a centrifugal field bioreactor
Authors: Voit Harald , Mersmann Alfons B. , Götz Friedrich
Published: August 2005

Fermentation under modified gravity could be of interest in application to (a) increasing productivity of growth and growth linked production with microorganisms at high cell densities and (b) increasing the productivity of highly viscous pseudoplastic polysaccharide fermentation. In both cases, higher oxygen transfer rates in centrifugal fields result in higher productivities since these fermentations are usually oxygen limited. A further aspect of fermentation under increased gravity is the reduction of foam since foam coalescence time decreases with acceleration number. On the other hand, under microgravity, shear reduction would allow growth and production even for very shear sensitive organisms. In order to carry out fermentations under modified gravity, a special type of fermenter–the centrifugal field bioreactor CFBR–has been developed at the Institute of Chemical Engineering (Head: Prof. Mersmann) of the Technical University of Munich. For the first time, exoprotein biosynthesis of lipase with S. carnosus has been carried out under sterile and controlled conditions in this novel bioreactor, in presence of increased mass forces.
Flow phenomena and local heat and mass transfer in corrugated passages
Authors: Gaiser Gerd , Kottke Volker
Published: August 2005

Flow phenomena, local heat and mass transfer and pressure drop of corrugated passages in process equipment are examined. Based on a method for measuring local heat and mass transfer, developed in previous investigations, a procedure has been formulated for the determination of local heat and mass transfer in corrugated passages. Using the analogy between heat and mass transfer, this technique allows the determination of heat transfer distributions in any structures with high local resolution. The corresponding pressure drop is presented together with the local and integral heat and mass transfer of different structures. It is shown that differences in heat and mass transfer as well as in pressure drop are due to different flow phenomena which also characterize mixing behaviour.
Evaporation rate and separation factor of molecular distillation in a falling film apparatus
Authors: Kawala Zdzislaw , Stephan Karl
Published: August 2005

During molecular distillation in a falling film apparatus, temperature and concentration of the more volatile components undergo a marked decrease in axial and radial directions, due to the distillation in vacuo. The gradients produce changes in the rate of surface evaporation and separation efficiency along the flow path. A theoretical study of this problem is presented for binary mixtures. The respective differential equations for heat and mass transfer in the liquid film are solved numerically. As the results demonstrate, the aspect ratio of an apparatus should be large when a high separation is required and small when a high distillation rate is more important.
On‐line measurement of partical size distribution and partical concentration in suspensions by ultrasonic spectrometry
Authors: Riebel Ulrich , Löffler Friedrich
Published: August 2005

The principle of ultrasonic spectrometry is based on the measurement of the ultrasonic extinction caused by the presence of particles. From measurements at different frequencies and with the knowledge of the ultrasonic extinction cross section of the particles, a system of linear equations can be established and solved to obtain the particle size distribution and particle concentration. With an experimental apparatus covering the frequency range from 1.7 MHz to 81 MHz, particles ranging from 20 to 1000 μm in diameter may be analyzed. The measurements can be carried out with particle concentrations as high as 10% by volume.
A study of gas and liquid distributions in structured packings
Authors: Stikkelman Rob , Teeuw Hessel , Wesselingh Hans , de Graauw Jan , Olujic Zarko
Published: August 2005

This study describes the gas and liquid distributions in a column with structured packings. The column is 0.5 m in diameter. It is equipped with a total of 1289 detectors in the top and bottom cross‐sections. These detectors provide a detailed picture of the gas and liquid flows through elements of only 25 × 25 mm2. The maldistribution in the gas bulk flow is negligible. Only the observed wall can contribute to malperformance. The gas flows in parallel to sheet orientation, thus introducing a radial transport. Together with the change in the orientation of subsequent packing elements, this results in good gas mixing. It was observed that the liquid wall flow rate decreases when the gas velocity exceeds 1.7 m/s. Up to the loading point, the maldistribution of the liquid is constant. Above this point, the equality of the distribution deteriorates rapidly, due to the occurrence of large‐scale liquid segregation.
Measurement of transient deformations by double‐pulsed holography
Authors: Hajduk Martin , Mewes Dieter
Published: August 2005

Holographic interferometry is used for the determination of surface deformation of items of equipment. The material failure which caused the surface deformation can then be identified. Because a double‐pulsed laser is used to plot the hologram, non‐vibration stabilized holographic equipment is necessary. Thus, non‐destructive testing of equipment components is also possible during plant operation. In this report, we present the experimental results of non‐destructive testing of composite materials. We examined centrifugally cast pipes and filament wound pipes, which were made from glass fibre reinforced plastic and carbon fibre reinforced graphite. As a rule, the severity of failure is characterized by the apparent perturbation of its holographically stored fringe pattern. In this report, we present the experimental results which yield the relationship between the perturbation of interference fringes and the extent of the specific types of failure. Measurement results were compared with displacements calculated by the finite element method. By using the interferogram, and with the knowledge of tension stress beneath the surface, the size of the crack can be estimated. The size of the smallest detectable flaw was clearly smaller than the critical flaw size. Thus, holographic interferometry is suitable for detecting damage to cylindrical containers.
Breakthrough behaviour of a binary gas mixture with azeotropic adsorption equilibrium
Authors: Persichini Carlo , Mersmann Alfons
Published: August 2005

This contribution reports on the breakthrough behaviour of binary gas mixtures with ideal and non‐ideal multicomponent adsorption equilibria. Investigations were carried out on mixtures CO2/C2H4 and C2H4/C2H6, both adsorbed on molecular sieve 5A (ms5A). The adsorption equilibrium of the system CO2/C2H4/ms5A may exhibit azeotropic behaviour, which subsides with decreasing active pressure (= sum of partial pressures of adsorbable components) or on raising the temperature. In contrast, the system C2H4/C2H6/ms5A maintains its ideal behaviour also at higher active pressures or lower temperatures. Attempts to calculate the non‐ideal adsorption equilibrium from measured single component isotherms have failed when known models were applied. The investigation of the effect of azeotropic equilibrium on the fixed bed adsorption led to intersecting breakthrough curves of the two components. This behaviour is due to a displacement of equilibrium caused by the change in the active pressure and partial pressures, and a superposed temperature effect. This can be shown by calculating the breakthrough curves with the equilibrium model.
Residence time distribution and hold‐up in a cocurrent upflow packed bed reactor at elevated pressure
Authors: van Gelder Klaas B. , Westerterp K. Roel
Published: August 2005

The residence time distribution in liquid phase was measured in a cocurrent upflow packed bed reactor for the system methanol‐hydrogen at low Reynolds numbers and at elevated pressure. The plug flow with axial dispersion model was used to describe mixing in the system. The imperfect pulse method was used to measure the system response to a tracer pulse input. The parameters were calculated using the weighted moments method. The influence of the weighting factor was investigated. The experimental and theoretical outputs, as calculated by convolution, agreed very well. Different types of correlations were used for the Bodenstein number and liquid hold‐up. From these correlations, the optimal one was selected for each parameter. A comparison was made between the ordinary moments and the weighted moments methods which led to the conclusion that the latter method is superior with respect to the accuracy of the estimated parameters and therefore strongly recommended.
On supersaturation during mass crystallization from solution
Authors: Kind Matthias , Mersmann Alfons
Published: August 2005

Supersaturation is the driving force for crystallization from solution. For design and operation of crystallization processes, it is necessary to apply a set of criteria for the determination of appropriate or even optimum supersaturation. In this paper we present and discuss the results of our experimental and theoretical investigations on supersaturation during crystallization from solution. While the determination of the metastable zone width of the solution is frequently applied as a fast check on solution behaviour, we demonstrate that the determination of the induction period of the supersaturated solution is a useful aid in ascertaining the maximum allowable supersaturation. Theoretical considerations and experiments confirm that the induction period dependssoley on growth kinetics if secondary nucleation is the predominant mechanism. In order to avoid uncontrollable spontaneous value of between 70 and 130 μm during crystallization. Since growth kinetics turns out to be the only important system property for the determination of maximum possible supersaturation, we conclude the paper with some arguments concerning a closed representation of growth kinetics.
Effect of nuclei storage and growth rate dispersion on the transient behaviour of continuous crystallizers
Authors: Heffels Stefan K. , de Jong Esso J.
Published: August 2005

Bench scale experiments and computer simulations of transient crystal size distributions obtained in a 1.4 m3 sucrose crystallizer, which prove the existence of nuclei stock, are presented. This stock represents a large number of non‐growing nuclei, which can be activated at increased supersaturations. The nuclei stock attenuates the dynamic behaviour of crystallization process.
Biological treatment of effluents from a coal tar refinery using immobilized biomass
Authors: Hüppe Paul , Hempel Dietmar Christan , Höke Hartmut
Published: August 2005

An airlift‐loop reactor with a fluidized bed was used for the microbiological removal of a complex mixture of aromatic substances originating from coal tar process waters. A specially adapted mixed microbial culture derived from several soil and sludge samples was immobilized on fluidized sand particles and retained in a reactor at high biomas concentrations of 3 to 16 g dry matter per liter, depending on the COD‐load. In a two‐stage pilot plant, those aromatic substances which passed through the first stage either unaltered or only partially oxidized were effectively eliminated by the immobilized biomass in the second stage. Whereas most of the waste water components such as phenols and quinoline were already degraded by a conventional activated sludge system in the first stage, the majority of nitrogen‐containing aromatic bases could be sufficiently eliminated with specially adapted micro‐organisms in the second stage. Although the COD‐feed load was increased to 12 and 15 kg m−3 d−1 in the first and second stages, respectively, it was removed to the extent of 87% on the average with an overall residence time varying between 11.5 and 29 h.
Modelling of a fluidized bed bioreactor for immobilized enzymes (Part 2)
Authors: Kiesser Torsten , Oerstzen Gustav A. , Bauer Werner
Published: August 2005

In the first part of this contribution, a mathematical model was presented for a liquid fluidized bed using immobilized enzymes, with reversible Michaelis‐Menten kinetics. This part is focused on the experimental results. The reaction kinetics of native and immobilized enzymes was determined in continuous stirred tank reactors under comparable conditions. The influence of external mass transfer was investigated in a fixed bed reactor column. The extend of pore diffusional resistance was examined in a continuous stirred tank reactor and with a numerical simulation. Hydrodynamics was measured in different reactor columns (diameter dt = 0.052 − 0.225 m; length L: 1.0–2.0m) and with a static mixer. Further, the concentration profile was determined in a fluidized bed reactor with side stream analysis for different biocatalyst samples, fluid velocities and bed heights. The simulation of experimental results indicates that they are well described by the developed model. Furthermore, the model is well suited to predicting the influence of specific parameters on the effective kinetics of the biocatalyst and the expansion of the fluidized bed.
Absorption of NO2/N2O4 in nitric acid
Authors: Weisweiler Werner , Eidam Klaus , Thiemann Michael , Scheibler Erich , Wiegand Karl Wilhelm
Published: August 2005

Laboratory‐scale measurements were performed on the absorption of NO2 gas into diluted nitric acid. The concentration of NO2 gas, which represents an NO2/N2O4 equilibrium, varied from 1000 to 20000 ppm, the carrier gas being nitrogen. The concentration of nitric acid ranged from 15 to 60 mass‐%. The absorption experiments were carried out in a double stirred cell, with a defined gas/liquid interface as the mass transfer area. The liquid phase was conducted periodically and the gas phase continuously. Mass flow rates were determined. The well‐known film model of absorption was used for analyzing the experimental results. Only the N2O4 species was considered to pass the gas/liquid interface. The measured data yielded values of H(k D1)1/2 as well as their variation with temperature and nitric acid concentration.
Critical temperatures and pressures and high temperature vapour pressures of seven alcohols
Authors: Lydersen Aksel L. , Tsochev Vassil
Published: August 2005

Critical temperatures and pressures have been determined experimentally for the four lowest n‐alcohols, 2‐propanol, 2‐butanol, and 2‐methyl‐1‐propanol, and are given in the penultimate line of Table 3. The last line of Table 3 lists the weighted mean critical pressures, with the corresponding critical temperatures obtained from he vapour pressure equation. Comparison with the corresponding data from standard reference books reveals deviations from the experimental data in some [2, 4] and incorrect critical pressure for ethanol in all five reference books quoted in Table 3. In addition, vapour pressure data were obtained for the same alcohols in the temperature range approaching the critical point. The measurements are reproduced by the simplified Clausius‐Clapeyron equation with the constants and standard deviation given in Table 2.
Influence of gas flow on heat transfer in film condensation
Authors: Numrich Reiner
Published: August 2005

For the dimensioning of condensers in film condensation, the heat transfer coefficient between film surface and cooled tube wall must be known. Generally, Nusselt equations are used which have been verified by experiments. When there is no significant gas flow, a large number of equations correlate the experimental. data very well. The description of heat transfer enhancement by a significant gas flow is not sufficiently covered by the available literature. For film wise condensation in a vertical tube, a calculation method is presented which reproduces this phenomenon characterized by the interfacial shear stress at the film surface. This method is based on the assumption that, in the proximity of gas flow, the condensation process also affects the interfacial shear stress. A comparison with known experimental local Nusselt numbers showed a good agreement with water as the fluid. For test fluid MWA, which was used by Blangetti, the measured values show only a moderate agreement with theoretical calculations. Possibly, this is related to entertainment which occurred during measurements at film Reynolds numbers of over 80.
Evaluation of plug flow assumption in packed beds
Authors: Foumeny Esmail A. , Pahlevanzadeh Hassan
Published: August 2005

Knowledge of modelling and computer simulation is an essential prerequisite for type design and operation of packed bed systems. Unfortunately, the existing models are based on a number of weak assumptions of which plug flow can be considered as a common deficiency. Such a simplification would inevitably have a noticeable bearing on the accuracy of the final design and consequently calls for the development of a coherent mathematical description of the packed bed systems so that reliable design information can be explored. A two‐dimensional heterogeneous transient model has been developed which allows for the radial variations of velocity and void age. The model equations have been solved using numerical approximation. The simulated results reveal significant differences between the present refined data and those established from existing plug flow models.
Measurements with multi‐point microprobes: Effect of suspended solids on the hydrodynamics of bubble columns for application in chemical and biotechnological processes
Authors: Wolff Christoph , Briegleb Frank Ulrich , Bader Joerg , Hektor Klaus , Hammer Hans
Published: August 2005

Many experimental studies reveal that suspended solids considerably alter the coalescence behaviour and hydrodynamic functions of wo‐phase flow. But no systematic efforts have yet been undertaken to separate the effects of different particle properties on local gas hold‐up, bubble size and interfacial area gas/liquid. The aim of this paper is to present the local values of these parameters in three‐phase fluidized beds of different solids, using miniaturized optical fiber and conductivity needle probes. It is shown that particle concentration, size and, in particular, density are decisive for the change in coalescence behaviour. Ranges of normal (ϱS > ϱL) and inverse fluidization (ϱS < ϱL) must be distinguished and the flow regime also exerts a strong influence on the interactions between the dispersed phases, the transition point itself being a function of particle properties can be observed, This effect is evaluated for different column diameters, between 0.1 and 0.3 m.
Growth rate dispersion in a continuous sucrose crystallizer and its effect on CSD
Authors: Gupta Bhaskar Sen , Dutta Tapas K.
Published: August 2005

A Random Crystal Growth (RCG)model is proposed to predict CSD in a continuous MSMPR crystallizer when the crystals exhibit growth rate dispersion. RCG model links two well‐known models of growth rate dispersion, namely the Random Fluctuation (RF) and Constant Crystal Growth (CCG) Models. Monte Carlo simulation has been employed to solve the model equations. Predicted results are compared with experimental CSD data on sucrose reported by Bennett.
Large‐scale anaerobic/aerobic treatment of complex industrial wastewater using immobilized biomass in fluidized bed and air‐lift suspension reactors
Authors: Heijnen Sef J. , Mulder Arnold , Weltevrede René , Hols Pam H. , van Leeuwen Hans L. J. M.
Published: August 2005

Warm concentrated industrial wastewaters are preferably treated in an anaerobic reactor for reasons of energy generation and low surplus sludge production. Problems to be solved in the practical application concern a low growth rate of the micro‐organisms, their low settling rate, process instability and the need for after treatment of the noxious anaerobic effluent which often contains NH and HS−. The use of biomass immobilized on small suspended carriers (< 0.5 mm) has proven to be a suitable means to overcome most of these problems. Results are presented on pilot and full‐scale pretreatment of industrial wastewater in an anaerobic 2‐state fluidized bed reactor for CH4‐production and laboratory and pilot scale post‐treatment of the anaerobic effluent, which contains NH and HS− in an aerobic air‐lift suspension reactor for the production of NO and SO.
Contribution to solving the problem of dioxins generated during waste incineration
Authors: Vogg Hubert , Hunsinger Hans , Stieglitz Ludwig
Published: August 2005

The production of dioxins/furans during waste incineration, and particularly the development of measures for minimizing the amount of generated pollutants, continue to command a considerable scientific as well public interest. Experiments are reported which were performed at the TAMARA municipal solid waste pilot incineration, erected on the premises of the karlsruhe Nuclear Research Centre. These experiments show that the solid waste mass flow rate and moisture content influence the dioxin/furan formation, Good removal efficiencies of dioxins/furans have been In wet cleaning. Hydrogen peroxide added to the crude gas is an interesting “killer” reagent for dioxins/furans.
Study on regeneration of diesel particulate filter using a laboratory reactor
Authors: Hoffmann Ulrich , Ma Jianxin
Published: August 2005

Regeneration of diesel particulate filters can be accomplished by complete combustion of a collected particulate. A reactor has been developed for study of the regeneration in the presence of catalysts, additives and ignition aids. This reactor allows an accurate measurement of soot ignition temperatures and a kinetic study of soot oxidation with an undisturbed soot layer and under a defined gas composition. Results of various investigations carried out with this reactor are presented.
Deasphaltization and demetalling of heavy crude oils and distillation residues with CO2
Authors: Eckermann Burkhard , Vogelpohl Alfons
Published: August 2005

Deasphaltization of heavy crude oils and distillation residues may reduce the metal content of these oils to such an extend that the upgrading of deasphaltized oil in a catalytic process becomes economically feasible. Experimental results of deasphaltization of Boscan crude from Venezuela, using subcritical and supercritical carbon dioxide as deasphaltizing agent, are presented. Deasphaltization and demetalling with CO2 in the supercritical state is more effective. Under favorable conditions, the deasphaltized oil contains practically no asphaltenes and the metal content is reduced by 690 wt‐%. The influence of n‐heptane or n‐pentane addition to the crude, which lowers viscosity and promotes flocculation, is also discussed. Furthermore, a multistage deasphaltization process is more efficient than a single stage process.
New and overlooked relationships for turbulent flow in channels
Authors: Churchill Stuard W.
Published: August 2005

This paper describes general, asymptotic and speculative relationships which can be deduced directly from the time‐averaged form of the basic, partial‐differential model for the conservation of mass and momentum in fully developed turbulent flow of constant‐property fluids through round and parallel‐plate channels. Such relationship are shown to provide insight as well as useful forms for correlation. Several analogies for flow in round tubes and between parallel plates which have generally been overlooked are reexamined and extended. A generally overlooked anomaly which occurs for flow in concentric, circular annuli, for flow between plates of non‐identical roughness, and for the combination of forced and wall‐Ind.uced flow between parallel plates is also is noted. The data needed to test the above analogies and to quantify the deviations, if any identified, as well as those needed to generalize the anomalous behavior.
Computation of plate columns for NOx absorption by a new stage‐to‐stage method
Authors: Wiegand Karl Wilhelm , Scheibler Erich , Thiemann Michael
Published: August 2005

A new stage‐to‐stage method has been developed for the calculation of NXx absorption columns. Each stage of the absorption column is simulated as a combination of a bubble column reactor (absorption) and an adiabatic plug for reactor (oxidation). The bubble column reactor is modelled as two single stirred tank reactors, one as a gas‐phase and one as a liquid‐phase reactor, both coupled by mass and heat transfer. In this hydrodynamic model, a dynamic approach is adopted, in which the gas‐phase transport of N2O4 is the limiting step for the absorption. A gas‐phasepseudo‐enhancement for factor for N2O4 is therefore introduced. The balance equations for a single phase of the bubble column are solved with a Newton‐Raphson algorithm. The entire column calculation is divided into a gas and a liquid side. On both sides, the stage‐to‐stage method is applied in such way that the overall calculation is performed as a loop process. The direction of the loop calculation follows that of the flow: gas‐side upwards and liquid‐side downwards.
Evaluation of standard thermodynamic parameters for the sorption of n‐hexane and methanol in zeolites
Authors: Pal Tapan Kumar , Majumder Asitava , Raha Tarun Kumar , Fetting Fritz
Published: August 2005

Adsorption isotherms for n‐hexane and methanol in mordenite and ZSM5 in the temperature range from 323 K to 473 K were found to be of type 1. The adsorbate‐adsorbent interaction (C1) and adsorbate‐adsorbate interaction (C2) wee computed according to Bradley and Wilkins model, whereas the Rees and Williams model predicts the adsorption characteristics. Finally, the thermodynamic parameters such as ΔGo, ΔSo, ΔHo, K, K+ have been evaluated for the sorption of n‐hexane in mordenite and ZSM5.
Heavy metal recovery by extraction and permeation in incineration preocesses
Authors: Bart Hans‐Jörg , Marr Rolf , Draxler Josef , Hartl Josef
Published: August 2005

Incineration processes are critical for the environment. SO2 and NOX removal with processes is nowadays commonplace. Up to now, heavy metal were recovered via precipitation. The alternative use of liquid ion exchange techniques offers an easy re‐use of the heavy metals, which are obtained as concentrates. A separation process is described, starting from laboratory experiments and ending with pilot plant field tests. A cost comparison for extraction, permeation and precipitation gives the scope of the necessary expenses for such environmentally controlled processes.
Modeling and simulation of reactions involving bifunctional catalysts
Authors: Schäfer Harald A. , Hoefer Eberhard P.
Published: August 2005

A mathematical model based on experimental results is set up for a typical model reaction of hydrocarbon reforming, namely the dehydroisomerization of methyl cyclopentane. Computer simulations shows that the existing theory about the reaction path of hydrocracking reactions involving bifunctional catalysts may be only partly valid.
Inertial deposition on front and rear sides of ribbons at intermediate and high reynolds numbers
Authors: Dau Günter
Published: August 2005

Deposition of particles from gas flows on ribbons in normally expected on the front side. Collision efficiencies of ribbons are presented for this case, obtained by means of single particle trajectory computation, which is based on numerically determined flow fields in the Reynolds number range between 2 and 50 and on the potential flow model. Further, it is shown, that deposition of particles on the rear side can be caused by eddylike motion of the fluid in the wake of the ribbon. For this to occur, two conditions must be fulfilled: the free shear layer between the wake and the outer flow must be turbulent to cause lateral transfer of particles into the wake and the Stokes number may not exceed 0.5.
The linear relationship between stoichiometry and dimensional analysis
Authors: Pethö Árpád
Published: August 2005

The linear algebraic character of the formal representation of chemical species and their reactions is compared with the procedure of searching for dimensionless numbers in a set of physical quantities. A straightforward algorithm is presented to find a finite set of solutions to the relevant system of “balance equations”, the so‐called minimal (or simple) solutions. At the third stage of the hierarchy thus established, “mechanisms” among reactions as well as “representations” among dimensionless group can also be defined.
Anodic dehalogenation of 1,2‐dichloroethane in aqueous electrolytes
Authors: Beck Fritz , Schulz Harry , Wermeckes Bernd
Published: August 2005

A solution of 0.1 M 1,2‐dichloroethane in 1 M H2SO4 was anodically converted to CO2, Cl2 and HCIO4 as the main products at smooth platinum. The current efficiency for CO2 exceeds 60% at low current densities, while HClO4 is obtained with about 20% current efficiency. Chlorinated products such as 1,2′,2‐trichloroethane are formed in negligible amounts. Platinum plays a distinctive role as anode material and shows a reaction limited anodic prewave. Our experimental findings lead to a mechanism, whereby DCE is initially hydroxylated to form chloroacetaldehyde chlorohydrin which releases HCl and becomes rapidly further oxidized to monochloroacetic acid. The cleavage of the CC bond proceeds via its anodic decarboxylation. Possible practical applications in the field of anodic water purification and in the direct electrosynthesis of vinyl chloride are discussed.
Some strategies for the kinetic study of complex heterogeneous catalytic reactions
Authors: Xu Jianguo , Hoffmann Ulrich
Published: August 2005

This paper presents a method of transforming the non‐liner regression problem in the kinetic study of complex heterogeneous catalytic reactions into a linear regression problem. Application of this method reduced the number of parameters to be estimated by n‐1, where n is the number of independent reactions. In addition, a stepwise model discrimination strategy in introduced to reduce the number of equation sets ad equations in the set undergoing parameter estimation. These two new approaches are very advantageous in reducing the computation effort, especially when the number of independent reactions is large. The linear regression method and the stepwise model discrimination strategy are successfully applied in the kinetic study of the methanol synthesis system in which the formation rates of methanol, methane, ethanol and ethane are considered.
The Markov process approach to modelling of residence of time distributions in flow systems
Authors: Kumar Surendra , Pethö Árpád
Published: August 2005

The Markov process approach, as used in the modelling of particle residence time distribution in a flow system of interlinked compartments, has been compared with the deterministic model of a complex reaction system of the first order. In the latter model, interfacial reactions take place between flowing phases, corresponding to the compartments in the stochastic model. It has been demonstrated that the two approaches are equivalent. A direct method of calculating the higher moments of the residence time distribution has been verified.
Effect of dispersions of CSD in continuous MSMPR crystallizers
Authors: Gupta Bhaskar Sen , Dutta Tapas K.
Published: August 2005

A general model is proposed to predict the crystal size distribution from multistage MSMPR Crystallizers taking into account shape factor, birth size and growth rate dispersions. Two cases, namely nucleation in the first crystallizer and the same process in all crystallizers have been considered. The developed equations can be solved easily by the Monte Carlo technique. The model represents an extension of the earlier work of Sen Gupta and Dutta.
Drop coalescence on inclined plates in liquids
Authors: Meon Walter , Blass Eckhart
Published: August 2005

Inclined plates are often installed as mechanical separation aids in gravity settlers for the separation of liquid‐liquid systems. The authors investigated the process of coalescence of single drops on trickling films flowing off inclined plates. The method of investigation was developed by Blass and Rautenberg. It ensures that, under certain conditions, only hydrodynamic parameters influence the coalescence process to any significant extent. The coalescence time of the drops characterizes the process of coalescence. Short time between 1 and 3 seconds provide favourable conditions for coalescence whereas long times, often ten times as long or even longer are unfavourable. This contribution introduces a criterion for clear demarcation between these two ranges and also a determination of separation parameters for favourable conditions for coalescence. Furthermore, the function of the plates is described, which is determined by hydrodynamic and wetting processes. The characteristic operating regions of a plate are shown in a working diagram.
An improved SRK‐equation for the estimation of concentrations by inferential measurements
Authors: Karlström Anders
Published: August 2005

A method is proposed for solving the vapour‐liquid equilibrium problem in binary distillation processes, when pressure and temperature are known. Special attention is paid to the applicability of the method for control purposes. Therefore, a comparison between measured and estimated concentrations is included for the case of propane‐propylene distillation. The method is based on an improved Soave‐Redlich‐Kwong equation of state and is easy to implement on a process computer. It yields a close approximation of experimental vapour and liquid volumes. On applying the original SRK‐equation at high pressures, an error in excess of 20% is obtained in the liquid volume which is one of the reasons why this equation cannot be used for control where high accuracy is required. In addition, the conventional mixing rule cannot reproduce the mole fractions correctly. Therefore, a new density‐dependent mixing rule is put forward for modelling of experimental results.
Apparatus for steady‐state kinetic measurements of the catalytic reduction of nitric oxide by ammonia on iron oxide
Authors: Claußen Michael , Kainer Hartmut , Kunz Ulrich , Hoffmann Ulrich
Published: August 2005

The reduction of nitric oxide with ammonia on an unsupported iron oxide catalyst has been studied in a continuous‐flow recycle reactor using simulated flue gas. The responses of the employed reactor system to step and pulse inputs of tracer indicate that the system could be regarded as a continuous stirred tank reactor (CSTR). Preliminary tests were carried out to determine the effect of temperature and particle size on the measured reaction rates. Additional experiments were performed in order to study the influence of oxygen and water concentration on these rates. A gas chromatographic system has been developed to analyze the gas components NO, N2O, NO2, NH3, H2O, O2, CO2 and N2. In addition, the concentrations of NO and NO2 were measured with a nondisperse infrared (NDUV/NDIR) analyzer.
Effects of sudden pressure changes in the surrounding gas phase on flow properties of bulk solids
Authors: Wiese Norbert , Schwedes Jörg
Published: August 2005

The variation in the behaviour of bulk solids as a result of sudden pressure changes in the surrounding gas phase is of interest in the application of lock hoppers for transfer of bulk solids into pressure vessels. By using such sluice systems, problems occur due to consolidation of the pressurized bulk solids. This paper presents the results of experimental and theoretical research, which allow to describe the influence of several parameters on pressure compensation and the degree of consolidation. With reference to the forces and mechanisms responsible for consolidation, it is possible to describe the different consolidation behaviour of incompressible (limestone) and compressible (hard coal) bulk solids.