List of Papers and Abstracts published during 19911992 in Speculations in Science and Technology in the section УDevelopments in Chemical EngineeringФ.код для вставкиСкачать
175 List of Papers and Abstracts published during 1991M992 in Speculations in Science and Technology, in the section: "Developments in Chemical Engineering I' (BookReviews and a Conference Listing are also included in each issue) Volume 14, Issue No.2,1991 Two Conceptual Problems in Heat or Mass Transfer to Arrays of Particles R. Ocone* and G. Astarita Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA Abstract: It is shown that the limit where the Peclet number approaches zero in an array of particles is a singular one. A simple cellular model is used, and the correct driving force for such a model is derived. When the Peclet number is finite, the Archimedes number is shown to determine the local relative motion; a modification of its definition is suggested for stirred tanks. An estimate of the dependence of the Nusselt or Sherwood number on the Archimedes number is derived from a scaling argument, and this is shown to be in reasonable agreement with published experimental data. (Pages 83-93). A Novel Approach to Flow Regime Prediction in Gas-Liquid Systems P.L. Spedding' and D.R. Spence Department of Chemical Engineering, The Queen $ University of Belfast, Belfast BT9 5AG, U K Abstract: Existing flow pattern maps and flow regime transition criteria are shown to be unable to successfully handle the effects of geometrical variations and changes in the physical properties of the phases. A new method is presented which is based on the separation of the flow patterns into either gas or liquid turbulence dominated flow. The individual flow regimes were identified by use of a number of parameters which together uniquely characterised regimes. Tests against crude oilhatural gas high pressure data were shown to be successful. (Pages 94-1 16). * Author to whom correspondence should be addressed. I76 Dispersion in Packed Beds: Does the Fluid Elasticity Play a Role? K.R. Westerterpl and R.J. Wijngaarden Department of Chemical Engineering, University of f i e n t e , PO Box 21 7, 7500 AE Enschede, Netherlands Abstract: For axial dispersion of mass in a packed bed at high fluid flow rates, the Bodenstein number is equal to two. This means that each cavity between two particles behaves as one mixing cell. In the region for turbulent flow for Reynolds numbers below 1000, the Bodenstein numbers for liquid flow and for gas flow differ by a factor of about 4. This indicates that axial dispersion of mass in a packed bed is not exclusively determined by the Reynolds number, i.e. the ratio of the kinetic energy over the viscous dissipation. Some other property, being different for gases and liquids, must also play a role. On the basis of the experimental observations of other scientists, and on the basis of own work on the axial dispersion of heat, it is speculated that in this case it might be the ratio of the intertia forces over the elastic forces, and not the Reynolds number, that governs axial dispersion in packed beds. (Pages 117-128). The Effect of Heat on Coal: An Annotated Bibliography (Part 1) C. Davies*, A.I. Porter and G.J. Rees Department of Science and Chemical Engineering, The Polytechnic of Wales, Pontypridd, Mid Glamorgan CF37 lDL, UK Abstract: A survey has been carried out of the effect of heat on coals up to approximately 900°C. The results have been interpreted in terms of the activation energies for the three main decomposition zones. The first decomposition zone appears to be associated with diffusion of trapped water and lighter components; the second by liberation of oily components; and finally the third region by active decomposition of the coal substance. The rate of heating, pre-treatment and physical structure of the coal, all influence the activation energies reported for the reactions. Catalysts influence the activation energies for the decomposition zones. (Pages 129-136). Heat Exchanger Design (1966-1990): A Bibliography (Part 1) Martyn S . Ray Department of Chemical Engineering, Curtin University of Technology, Perth, Western Australia Abstract: Heat exchanger design is of fundamental importance to both chemical and mechanical engineers. The evaluation, specification, and design of heat transfer equipment occurs in many unit operations of chemical processes. Over the past 50 years a significant proportion of the published technical literature has been concerned with heat transfer fundamentals and applications, and heat exchanger design and operation. This two-part article is a bibliography of published papers (and some books) on selected heat exchanger topics for the period 1966-1990. The topics included are: Part I: Heat Exchanger Design: Part 11: Heat Exchanger Operation, Heat Exchanger Applications, Plate Heat Exchangers 177 The information contained in this paper provides an in-depth coverage of heat exchanger design for the past 25 years. References for the past two years (1988-1990) were included to update those taken from a new bibliography prepared by the author. The recent paper by Eckert et al. is a useful review of the fundamental heat transfer literature (for 1989). (Pages 137-147). Volume 14, No.3, 1991 Oxygen Chemisorption on a Laboratory-coked Resid HDS Catalyst Y. Wang, J. Baumgart, W.R. Ernst* and J.D. Carruthers School of Chemical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA Abstract: Samples of a commercial CoNolalumina resid HDS catalyst were coked to progressively higher levels with styrene at 425°C. TGA was used to determine coke content of the samples. Oxygen uptake at 0°C increased with increasing coke content, while BET surface area decreased. The results suggest that coke preferentially blocks surface which has the lowest density of oxygen adsorption sites. (Pages 164-170). The Effect of Heat on Coal: An Annotated Bibliography (Part 2) C. Davies*, A.I. Porter and G.J. Rees. (Pages 171-176). Heat Exchanger Design (1966-1990): A Bibliography (Part 2) Martyn S . Ray. (Pages 177-185). Volume 15, No.l,1992 Effects of the Microporous Polymer-Supported Catalyst on the Allylation of 2,4-Dibromophenol M.-L. Wang' and C.-C. Yu Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan Abstract: The reaction of allyl bromide with 2,4-dibromophenol in an organic solvent/aqueous solution to synthesize 2,4-dibromophenyl allyl ether by triphase catalysis was studied. The microporous polymer pellet which served as the support of the catalyst was prepared by reacting styrene monomer with chloromethyl styrene and divinyl benzene in a suspension polymerization reaction. Tri-n-butyl amine was then immobilized on the surface of the polymer pellet to form the three-phase phase transfer catalyst. Immobilization of the catalyst on the polymer support should be carried out by mechanical agitation in order to obtain a high catalyst reactivity. In the three-phase reaction, the effects of agitation speed, solvents, alkali concentration and the characteristics of the triphase catalyst on the conversion of allyl bromide were investigated in detail. I78 On the basis of the experimental data (using 2.28 g of 2,4-dibromophenol), the optimum operating conditions for preparing the triphase catalyst in order to get a higher yield of 2,4-dibromophenyl ally1 ether were: (a) using a low degree of polymer cross-linking (2%); (b) a smaller particle size; (c) 2 g of KOH (50 mL of H20); (d) 1.5 g of triphase catalyst; (e) 50 mL of dichloromethane solvent; (f) stirring speed greater than 400 rpm. (Pages 3-14). Properties of the Crystal Size Distribution Estimated from Density-Distribution Functions J. Mydlarz* and D. Briedis Department of Chemical Engineering, Michigan State University, East Lansing, MI 48824-1226, USA Abstract: A discussion of the properties of the crystal size distribution (CSD) estimated from both simulated and real MSMPR crystalliser population density distributions is presented. In the case of simulated linear log population density versus size data, estimation of characteristic parameters of the particle distribution from the population density distribution give values of the parameters which are close to their theoretical values. Calculations indicate that for real CSD-MSMPR crystalliser data, the values of the means of particle population are significantly related to the particle size range measured. This is particularly important in the lower range of the estimated means of experimental population density data. Estimation of the kinetics of growth and nucleation also confirms that values of crystal growth and nucleation rates for the same run are substantially related to the crystal size range measured. (Pages 15-23). Prediction of Emulsifiability of Viscous Crude Oils with Alkali Treatment from Interfacial Tension Measurements J.P. Giordano, S. Magdassi, S.G. Frank, D.H. Fruman and J.L. Zakin' Department of Chemical Engineering, The Ohio State University, Columbus, OH 43210, USA Abstract: Viscous crude oils will provide a valuable source of future oil supply as low viscosity crudes are depleted. A promising technique for transporting them to refineries is as low viscosity concentrated oil-in-water emulsions. Of six heavy crudes tested, 60% oil-in-water emulsions could be prepared from three of them by treatment with sodium hydroxide over a fairly wide alkali/total acid number (TAN) range. Relatively unstable emulsions over a narrow range of sodium hydroxide addition could be formed from one crude, and emulsions could not be formed with the other two at any alkali level. Interfacial tension measurements of 90% crude in toluene solutions against 0.01% sodium hydroxide solutions gave results below 0.003 N/m for the three crudes that could be emulsified, and over 0.0068 N/m for the other three, indicating that such measurements can be used to predict the feasibility of preparing emulsions by alkali treatment. Measurements at 77% crude in toluene confirm these findings but the absolute values are generally somewhat higher. (Pages 24-29). 179 Lenticular Drops: A Key to Lmmiscible-LiquidTransport in Aquifers? C.D. Rugge, R.C. Ahlert' and J.M. Zukowski Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ 08855-0909, USA Abstract: Denser-than-water, immiscible chlorinated solvents (DNAPLs) may spread through the unsaturated zone after spillage, eventually penetrating the saturated zone. A tendency of DNAPLs to float on air-water interfaces may cause these liquids to be distributed at the capillary fringe. A study was performed with 1,1,1 -trichoroethane, 1,1,2-trichloroethane, tetrachloroethylene, carbon tetrachloride and trichloroethylene to investigate the mathematical dependence of the maximum stable volume (MSV) of solvent that can remain floating at an air-water interface with the Bond number (Bo), a dimensionless quantity incorporating density, interfacial tension, and aperture radius. It is proposed that MSV is a function of (Bo - Bo*), where Bo* is a critical Bo below which no MSV forms. This critical-mass model may have application in describing DNAPL transport in aquifers, incorporating both fluid and aquifer properties. (Pages 30-39). Volume 15, No.2, 1992 Present Trends in Process Safety Trevor A. Kletz, Senior Visiting Research Fellow University of Technology, Loughborough, Leics LEI1 3TU, UK Address for Correspondence: 64 Twining Brook Road, Cheadle Hulme, Cheadle, Cheshire SK8 5RJ, UK Abstract: Recent developments in process safety are reviewed. Hazard and operability studies (hazop) and hazard analysis continue to grow in popularity and computerised aids are now available. The limitations of the conventional hazop of a line diagram are becoming recognized: it is carried out too late in plant design for fundamental changes to be made. If we can carry out similar studies earlier in design then we can design inherently safer and more user-friendly plants which can tolerate human error or equipment failure without serious effects on safety (and output and efficiency). It is now recognized that we should remove opportunities for error and not expect people to be error-free. Computer control has provided new opportunities for old hazards. Companies are still reluctant to learn the lessons of the past and many senior managers do not see that they have a part to play. (Pages 83-90). Relationship between Drop-Size and Field Strength in Enhanced Whole-Broth Liquid-Liquid Extraction L.R. Weatherley Department of Chemical Engineering, Heriot Watt University, Riccarton, Edinburgh EH14 4AS, U K Abstract: Recovery of products from microbiological fermentation systems by direct solvent extraction offers significant scope for process simplification and reduction in production costs. The use of electrical fields to accelerate the slow 180 kinetics of whole-broth extraction offers the potential for a viable and cheap alternative to mechanical enhancement methods. This study was aimed at determining the drop behaviour during extraction by comparison with a known model system. The relationship between drop size, nozzle velocity, physical properties and applied field strength was explored for single aqueous drops dispersing from a nozzle into an organic solvent under the influence of a constant electric field. The behaviour of the system ethanol-waterh-decanol was compared with that of fermented malt extract liquorh-decanol i n the presence of Saccharomyces cerevisiae. The experimental measurements of drop size were compared with theoretical predictions based on a model in which the effect of electrostatic forces acting upon detaching drops is described in terms of the nominal field strength and the length of the charged nozzle. Good agreement between the experimental and predicted drop sizes was found for both liquid-liquid systems. (Pages 91-100). Effect of Energy Input on Bubble Coalescence in Bubble Columns M. Jamialahmadi and H. Miiller-Steinhagen' Department of Chemical and Materials Engineering, University of Auckland, Auckland, New Zealand Abstract: This paper combines the results of several investigations aimed at obtaining a better understanding of bubble coalescence in order to control this unwanted phenomenon in bubble columns. The effects of different methods of energy input, i.e. heating, vibration and agitation on bubble coalescence and bubble break-up have been analysed. Gas and liquid-phase flow patterns have been examined. From these results, it was found that if liquid backmixing can be reduced in some way, such as radial baffling or decreasing column height, then the bubble coalescence decreases and therefore, the gas hold-up increases significantly. (Pages 101-1 10). Design of Decouplers and Feedforward Compensators in the Presence of Unrealizable Time Delays P.R. Krishnaswamy', N.V. Shukla and P.B. Deshpande Department of Chemical Engineering, National University of Singapore, Kent Ridge, Singapore 0511 Abstract: Unrealizable time delays (positive dead time) can cause a significant deterioration in the performance of feedforward compensators employed in multivariable decoupling control and SISO applications. In this paper it is shown that the performance of such systems can be considerably improved, contrary to general belief, by judicious addition of pure time delay to the system. This concept is illustrated with two simulation examples. One is a 2 x 2 boiler control system exhibiting one way interaction, and the other is a heat exchanger operating under combined feedback/feedforward control. The results from the boiler example show that loop interaction can be completely eliminated while at the same time loop integrity is preserved. In the case of the heat exchanger, a remarkable improvement in feedforward action is realized without affecting the stability of the closed loop system. (Pages 111-1 19). 181 Volume 15, No.3, 1992 Chemical Process Simulation Packages M.A. Hussain Department of Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia Part I: A Guide to Selection Abstract: Computer-aided chemical process modelling and simulation has become an integral part of chemical engineering practice. It is widely used in academic institutions and by many engineers in research and development, as well as in process and plant engineering situations. Many simulation programs are now commercially available, coupling the technical rigour of the most sophisticated modelling and simulation systems with ease of use. The range of simulation packages now available has created a need to choose the right software at the right time with the right cost. This paper discusses the important factors to be considered when choosing a general process simulator, with more emphasis towards the personal computer-based programs. An example of the use of such a simulator for a particular application, and to demonstrate certain features, is described in Part I1 of this paper. (Pages 163-170). Part 11: A Case Study Example Abstract: Many chemical process simulation packages have been developed in the universities and industry since the 1960’s, mainly for use on mainframe or minicomputers. However, with the latest upsurge of powerful microprocessor technology many of these simulators have been converted for use on the personal computer. This paper assess the salient features of the PC-based DESIGN I1 simulation package, with a case study application for a plant producing cyclohexane by catalytic hydrogenation of benzene. A comparison with results obtained using the FLOWTRAN simulator is included. (Pages 171-178). Continuous Electrolytic OxidatiodReduction of Fe(II)/Fe(III) Ions in Uranium Ore Leach Solutions I. Nirdosh Department of Chemical Engineering, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada Abstract: In the ferric chloride leaching process of uranium ores, uranium dissolves predominantly in the uranyl cation form U02 ’+. Reduction of the abundant ferric ion present in the solution to the ferrous state is necessary prior to the recovery of uranium from the leachate by solvent extraction, in order to minimize the uptake of ferric ions by the solvent. The recycle of aqueous solution for leaching after the solvent extraction operation requires re-oxidation of the ferrous ions to the ferric state. A continuous flow-through diaphragm electrolytic cell has been tested for simultaneous oxidation of the ferrous ions in the anodic side, and the reduction of the ferric ions in the cathodic compartment of the electrolyzer. It was found that the cell operates successfully and the cell voltage depends primarily on the ohmic losses. (Pages 179-185).