摘要:

AbstractReasons are given why the axial dispersion in a gas flowing through a packed bed may be influenced by the elasticity ‐ or compressibility ‐ of the fluid. To support this hypothesis, experiments have been done in a packed column at pressures from 0.13 to 2.0 MPa. The elasticityEof a gas is proportional to the pressurePand the compressibility to 1/P. The axial dispersion coefficients as determined were found to be a function of the pressure in the packed bed in the turbulent flow region of 3

ISSN:0930-7516    

DOI:10.1002/ceat.270190402

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe results of simulations of direct concentration control of a distillation column in industrial scale are presented. Both controlled variables, the two product concentrations, are determined by on‐line gas chromatographs and are characterised by high dead times of about 30 min. For the resulting scanning control of the product concentrations corresponding decentralised PI controllers were developed and applied. The control of the product concentrations developed presents a conventional DV structure and was exemplarily tested for disturbances in feed flow and feed concentrations. The calculations carried out exhibit a good time behaviour of the whole system. On this occasion it can be stated that the control quality could be clearly improved if a steady‐state decoupling by output transformation was employed. In this case the results achieved are totally comparable to those of internal model control (IMC), which was in use at the production plant for over two ye

ISSN:0930-7516    

DOI:10.1002/ceat.270190403

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA random packing hydrodynamic simulator is designed specially to carry out experiments under reduced pressures with a counter‐current flow air/water system. The simulator results (air/water system) compared to those obtained in a real packed distillation column (benzylchloride/ ethylbenzene system) show a good agreement between hydrodynamic parameters like pressure drop, flooding flow rate, and total liquid hold‐up. Empirical relationships derived from the simulator experimental results are proposed allowing the calculation of the pressure drop in a packed distillation column, operating in the pressure range between 10 kPa and atmospheric pressure. The influence of reduced pressure on the HETP in the distillation column and interfacial area in the simulator was also investiga

ISSN:0930-7516    

DOI:10.1002/ceat.270190404

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIntermig impellers have been postulated as very efficient for mixing highly viscous non‐Newtonian fluids (such as xanthan and mycelial broths). However, no formal characterisation has been published and no fair comparisons have been made, based on accurate power drawn measurements and using equal number of impeller stages and equal diameter, if compared (for example) with the performance of Rushton turbines. Characterisation of the shape, size, and evolution of the well‐mixed zones or “caverns” were correlated with power drawn, for single and dual Rushton turbines and for one‐ as well as two‐stage Intermig unslotted impellers. Cavern evolution studies were carried out in a mixing tank (diameter=0.205 m,H/T=1.6) equipped with an accurate air bearing dynamometer. Carbopol 940 (0.25 wt.‐%) was used as a model, transparent fluid. Impeller to tank diameter ratio was 0.53 for both impellers. Caverns were visualised by injecting methylene blue in the well‐mixed zones. A single Rushton turbine developed larger caverns if compared with one‐stage Intermig of the same diameter under power drawn below 1.5 kW m−3. At higher power drawn, both impellers behaved very similarly, reaching a limit in cavern volume of about 40% of the total liquid volume, even at very high (20 kW m03) power drawn. A similar trend characterised dual combinations: below 3 kW m−3, dual Rushtons gave larger cavern volume if compared with the performance of two‐stage Intermigs. In either case, power drawn higher than 3 kW m03was sufficient to mix more than 90% of the liquid volume. The presence or absence of the slot in the Intermig did not influence cavern development. Experiments with a smaller if compared with those obtained with the larg

ISSN:0930-7516    

DOI:10.1002/ceat.270190405

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThis article presents gas kinetic calculation methods for the energy transport in hydrogen/ air and methane/ air mixture. The total molecular heat conductivity as well as its various shares are calculated and discussed for a temperature range of 400 to 3500 K and for a pressure of 105Pa. The variation of the air/ fuel ratio under the conditions of chemical equilibrium is also investigated. As opposed to our previous article, an extension of the Chapman‐Knskog method which goes beyond the classical 1st approximation for elastic collisions is applied for the evaluation of suitable calculation methods. This is carried out following the method for strong relaxing thermal nonequilibrium according to Brun. The equations applied in this work are simplified formulations for the proximity to equilibrium. The method for the evaluation of the parameters of the inelastic collision and some chosen results are presented. A discussion of the various shares of the molecular heat conductivity emphasizes the considerable influence of the diffusion and the thermal diffusion processes in fuel/ air mixtures compared to the Fourier heat conductivit

ISSN:0930-7516    

DOI:10.1002/ceat.270190406

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA unified gas/ solid reaction model has been formulated for multi reactions with multi gas and solid species. The transient formulation has been followed by finite‐difference method and subsequent solution via an iterative procedure. The simulation produces intermediate results for concentration profiles of various components and pressure and temperature distribution, in addition to various structural parameters within a reacting pellet. The effect of structural parameters is analysed. The general formulation allows homogeneous and heterogeneous reactions. Solid state processes can also be accommodate

ISSN:0930-7516    

DOI:10.1002/ceat.270190407

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper deals with the modeling of toluene adsorption in a technical column of activated carbon in a low concentration range (2.6 to 3.4·10−3kg/m3), which is usual for environmental applications. It is also concerned with methods of numerical solutions of the nonlinear partial differential equations (PDE), a modified control volume method was used to determine the PDE. Three nonequilibrium isotherm models are developed to describe mass transfer in a fixed bed of activated carbon (Degussa WS‐4). The important parts of this paper are the simulation of the maldistribution of concentration and loading of the pollutant in the technical column, as a result of the flow velocity maldistribution and the study of the mass transfer mechanisms in a technical fixed bed. It is found that in a low concentration range, toluene adsorption in a fixed bed of activated carbon (Degussa WS‐4) is an external rate‐controlled process, thus surface diffusion cannot be neglected. The calculated results are in good agreement with the experimental ones. The measured effect of an earlier breakthrough near the wall‐near zone has been calculated using

ISSN:0930-7516    

DOI:10.1002/ceat.270190408

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAffinity separation can be achieved by batch and fixed bed modes. Mathematical models including film mass transfer, intraparticle diffusion, and reversible reaction are formulated for both fixed bed and batch adsorption processes. Orthogonal collocation method is used to numerically evaluate the performance of batch and fixed bed adsorption. The efficiencies are evaluated in terms of both the solute recovery and adsorbent utilization. The effect of the following parameters is simulated for the comparison purpose: solute concentration, reaction kinetics, ligand content, and particle size. Fixed bed mode is found to be efficient.

ISSN:0930-7516    

DOI:10.1002/ceat.270190409

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractCalcination and carbonation behaviour of dolomite has been studied in a pressurised thermo balance at pressures in the range of 1.1 to 2.3 MPa and for temperatures ranging from 730 to 840°C. The atmosphere consisted of nitrogen containing up to 20 vol.‐% carbon dioxide. The calcination of dolomite has been studied as a function of temperature, particle size, andPco2. An investigation concerning possible mass transfer restrictions for the experimental system and a model investigation of the calcination rate in CO2atmosphere has been made. Further, the effect of calcination on the BET surface and the BET surface including the surface structure due to successive temperature cycles has been studied. The temperature for the initialisation of calcination of dolomite in CO2atmosphere was independent of bothPco2and the particle size. No conclusive indications on mass transfer restrictions have been detected for the experimental system. A significant difference in calcination rate as a function of particle size existed for decomposition in CO2atmosphere. A model for homogeneously progressing chemical reaction parallel with a shrinking core chemical reaction together with a mass transfer control mechanism was found to describe the calcination rate in CO2atmosphere most accurate

ISSN:0930-7516    

DOI:10.1002/ceat.270190410

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractExperiments on thermal decomposition of calcium carbonate were carried out in a thermogravimetric analyser under non‐isothermal conditions of different heating rates (10 to 100°C/ min). A new technique for determining the kinetic parameters from non‐ isothermal thermogravimetric data was described. The activation energy and frequency factors were determined from the proposed method and also by the widely used Coats and Redfern method. The kinetic compensation effect between the activation energy and frequency factors obtained from both the methods were found to be very consistent and are in very good agreement with the literature values. The activation energy and frequency factors were also determined from isothermal experiments in the temperature range from 680 to 875°C. The activation energy and frequency factors determined from isothermal data using initial rate method were also found to be in very good agreement with the above results. It is also found that the kinetic parameters determined by isothermal analysis were consistent with the values determined by non‐isothermal a

ISSN:0930-7516    

DOI:10.1002/ceat.270190411

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY