摘要:

AbstractInterfacial areas and gas hold‐ups were determined at pressures of up to 1.7 MPa in a glass vessel, 88 mm in diameter and of standard geometry. Superficial gas velocities between 0.25 and 2.0 cm/s were used and the stirring speed varied between 4 and 30 rps. The interfacial areas were determined by the chemical method, using the model reaction between CO2and aqueous diethanolamine (DEA). Hold‐ups were determined by observation of differences in height. In contrast to literature indications, the gas hold‐up was found to be independent of reactor pressure. This is also true for the interfacial

ISSN:0930-7516    

DOI:10.1002/ceat.270110102

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractDesign and operation of a circulating fluidized bed requires the knowledge of fluid mechanics. According to heat and mass transfer as well as chemical reactions, the effect of the set superficial gas velocity on the axial pressure profile is of particular interest. The axial pressure profile was measured for a variety of solids, as a function of the superficial gas velocity, in a cylindrical circulating fluidized bed with an inner diameter of 0.19 m and an overall height of 11.5 m. Depending on the solids content and superficial gas velocity, two or one sections can be observed in the plant where the pressure gradient is constant. A pressure profile with one pressure gradient exists only at high gas velocities, so long as the acceleration pressure drop immediately above the gas distributor is negligible. Comparison of measured pressure drops in circulating fluidized beds with those measured in vertical pneumatic conveying led to a state diagram for vertical gas‐solid flows. The operation behaviour of different types of circulating fluidized bed plants can be explained with the aid of this diagra

ISSN:0930-7516    

DOI:10.1002/ceat.270110103

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractCrossflow microfiltration (CMF) is a pressure driven membrane process for the separation of suspended microparticles, bacteria and emulsion droplets. The fluid to be filtered flows in parallel to the membrane surface and restricts the formation of a filter cake. This contribution explains the basic process characteristics and the combination of the crossflow technique with other membrane cleaning methods (periodic backflushing, chemical cleaning). Special attention is paid to the influence of different process parameters on the flux through the membrane. The principle of plant design and different operation modes are described. Engineering aspects such as hydrodynamics, energy requirement and selection of construction materials are discussed in some detail.

ISSN:0930-7516    

DOI:10.1002/ceat.270110104

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractWhile two‐ and multiphase flows find more and more application in chemical engineering practice, and the demand for theoretical information about mass and heat transfer processes in such systems is increasing, such data or at least experimental results which could be generalized are still lacking. The following pages are concerned with mass transfer in laminar suspension tube flows normal to the main direction of flow due to the individual motions of small, inert spherical particles. On the basis of a large number of experimental data, an interpretation is attempted of the role of nearly neutrally‐buoyant particles in mass transfer enhancement, and a model for a semi‐empirical description is suggested. The experimental arrangement uses the mass transfer of carbon dioxide in laminar flow of salt water during the process of gas permeation through a permeable membrane tube

ISSN:0930-7516    

DOI:10.1002/ceat.270110105

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractFischer‐Tropsch catalysts (Fe/V oxides with ZnO and K2CO3as promoters) were exposed to CHCl3, thereby producing surface and bulk chlorides. The effect of this exposure on activity and selectivity was studied in a continuous recycle reactor at a total pressure of 10 bar (CO/H2in most experiments: ca 1:1) in a temperature range between 200 and 343°C. CHCl3was introduced in amounts of up to 1 × 10−2mol chlorine per g catalyst. The catalyst samples were characterized by internal surface area, pore‐size distribution and adsorption capacities for CO, H2and C2H4. Prior to synthesis, the catalysts were reduced by H2. Catalyst exposure to CHCl3resulted in a decrease of activity and considerable changes in product distribution. Hydrogenation and isomerization of1‐olefins were partly suppressed; the chain length of the products was slightly increased. Deactivation of the catalysts due to chlorine addition was partly reversible during operation, while olefin formation was not significantly altered with time‐on‐stream. The effect of chlorine on activity and selectivity is explained by dissociation of CO as the chain initiating step and CO insertion into a carbon/metal bond as a possible chain propagation step. Since adsorption capacity for H2decreases on the addition of chlorine, this may also contribute to lower activity and change in selectivity, compared to the unexp

ISSN:0930-7516    

DOI:10.1002/ceat.270110106

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractAn important parameter influencing the crystal size distribution in mass crystallization from solution is the mechanical stress exerted on crystals in the crystallizer. This contribution presents the study of the influence of mechanical stress and attrition of the system potassium nitrate‐water in an FC‐crystallizer and in various draft‐tube crystallizers, fitted with different types of impellers. The intensity of stress is a newly defined variable which is used to describe the level of stress in crystallizers. The reduction of crystal size by attrition is described by the linear attrition rate. The influence of impeller design and crystal hold‐up on crystal size distribution and scale‐up rules is

ISSN:0930-7516    

DOI:10.1002/ceat.270110107

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe performance characteristic of a packed bed reactor has been analyzed by considering diffusional resistance of the biofilm. Model equations were solved by the method of orthogonal collocation for various classical enzyme inhibition kinetics, including partially non‐competitive, partially competitive, partially uncompetitive, partially mixed and fully mixed. For all considered modes of inhibition, an increase in the inlet substrate concentration decreases the steady state conversion in the reactor. However, an increase in the Peclet number has been found to improve the conversion. The effects of various other process variables of physical importance were also investigated parametricall

ISSN:0930-7516    

DOI:10.1002/ceat.270110108

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA single variable pole‐placement self‐tuning controller (PPSTC) is used to simulate examples typical of chemical processes; i.e., open‐loop stable, unstable, and unstable non‐minimum phase systems with unknown varying process dead time. The PPSTC is shown to be effective in each case. Set‐point tracking and rejection of randomly occurring deterministic disturbances for all three types of processes are achieved. Simultaneous estimation of process parameters and process time delay is realized by using a recursive extended least squar

ISSN:0930-7516    

DOI:10.1002/ceat.270110109

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractAsymptotes are known to be useful, but their potential in interpreting and correlating chemical and physical behaviour is seldom exploited fully. The derivation and selection of asymptotes for particular as well as limiting cases is described. The evaluation of the range of validity and applicability, if any, of asymptotes is also considered. Asymptotes are shown to be uniquely useful in the identification of groupings of variables which minimize parameteric variations, as upper and lower bounds, as trial functions in the method of weighted residuals, and most especially as components of correlating equations.

ISSN:0930-7516    

DOI:10.1002/ceat.270110110

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA pilot wet scrubber was examined experimentally. It is constructed like a plate column. Its plates are designed to set the gas into a whirling motion with tangential velocities of up to 25 m/s and to ensure a uniform distribution of the liquid throughout the gas flow. Particles suspended in the waste gas are collected by gas‐atomized droplets to yield cut diameters between one and two microns. Energy consumption is lower than in the case of other scrubbers. The scrubbing mechanisms are analyzed by examining the measured pressure drops. Finally, methods of determining the collection efficiency are discussed and an empirical approach to its calculation is presente

ISSN:0930-7516    

DOI:10.1002/ceat.270110111

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY