Noncatalytic Gas-solid Reactions Research Articles

Evolution of pore surface area during noncatalytic gas-solid reactions. 2. Experimental results and model validation

Mesures de la cinetique et de la modification de la structure poreuse au cours de la gazeification avec O 2 et CO 2 de trois semi-cokes de charbon bien caracterises. Ces resultats sont utilises avec d'autres pour valider les modeles aleatoires de porosite predisant l'evolution de l'aire superficielle des pores a l'aide de proprietes structurelles mesurables sur le solide a l'etat brut

Evolution of pore surface area during noncatalytic gas-solid reactions. 1. Model development

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEvolution of pore surface area during noncatalytic gas-solid reactions. 1. Model developmentGirish Ballal and Kyriacos ZygourakisCite this: Ind. Eng. Chem. Res. 1987, 26, 5, 911–921Publication Date (Print):May 1, 1987Publication History Published online1 May 2002Published inissue 1 May 1987https://doi.org/10.1021/ie00065a011RIGHTS & PERMISSIONSArticle Views183Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Boundary layer analysis for the modeling of noncatalytic gas-solid reactions

Several distributed models are available in the literature for estimating the rates of noncatalytic gas-solid reactions. These models are all based on the consideration of the same basic phenomena, but different simplifying assumptions are made in each; the Most common simplification is the quasi-steady-state approximation. the general model where no simplifying assumptions are made is discussed iN this paper. In its dimensionless formulation, it contains two parameters. It is shown that as the values of these parameters approach zero or infinity, some of the simplifying assumptions are justified in a well-defined asymptotic sense.

Transient analysis of the particle-pellet model with structural changes in the solid phase

A transient analysis based on the particle-pellet model, which includes the effect of structural changes is presented for non-catalytic gas-solid reactions. Changes in the conversion-time relationship and in temperature profiles in the pellet are considered. The numerical solution of the resulting non-linear partial differential equations is performed using the method of lines, whereby finite difference discretization in the spatial variable yields a stiff system of ordinary differential equations in the time variable. The resulting initial value problem is solved with a general-purpose ordinary differential equation solver. The results obtained using this transient model have been compared with those using a simplified model in which a pseudo-steady state is assumed. Significant differences were found for cases in which structural changes are large.

A comparative study of mathematical models for gas-solid non-catalytic reactions

Experimental data on desulphurisation of a simulated coal gas mixture containing 200 ppm H2S, using CuO/ZnO mixed oxide sorbent in a fluidised bed reactor, are used to evaluate four representative structural models for gas-solid non-catalytic reactions. The four models chosen for evaluation are the spherical changing-grain-size model of Georgakis and co-workers, the rectangular grains version of the general formulation of Szekely and co-workers, the single-pore model of Ramachandran and Smith and the random pore model of Bhatia and Perlmutter. All the model parameters except the reaction rate constant are calculated from experimental measurements or from literature correlations. The rate constant alone is adjusted so as to obtain good agreement between the model and the experiment. It is shown that at any given temperature all the models describe the data well. However, the random pore model predicts conversions lower than experiment at large times while the rectangular grains model predicts conversions higher than experiment for small times. The rate constants decrease as temperature increases indicating an inadequacy of all the models in this regard. The models also predict much smaller variations in conversion with change in particle size than those observed experimentally.

Analysis of non-catalytic gas-solid reactions in a vertical transport reactor

Vertical transport reactors are analysed for gas-solid conversions in terms of the plug flow of gas and solid particles and in terms of the shrinking core model for the non-catalytic gas-solid reaction. An approximate analytical solution is given for the gas-solid conversions. The proposed solution is simple and computationally easy and the length of the reactor required for a given conversion is calculated directly. The proposed solution is compared with the reported exact analytical solution which is cumbersome and computationally difficult and in which the length of the reactor can be obtained only by iteration. The agreement between the proposed approximate solution and the exact analytical solution is good. Furthermore, the minimum in the plot of the gas conversion versus the particle diameter shows interesting behaviour.

Gas-solid reactions: A method of direct solution for solid conversion profiles

A new solution technique for non-catalytic gas-solid reactions, which are first order in gas concentration but are represented by any general rate form with respect to the solid, has been proposed. An equation for the variation in conversion with position in the pellet has been derived, the solution of which yields the conversion profiles and the average conversion directly. The method has been illustrated by application to a number of models, such as the particle pellet model with and without structural changes, the volume reaction model, and reactions with significant nucleation effects.

Percolation concepts in modelling of gas-solid reactions—I. Application to char gasification in the kinetic regime

The application of percolation theory to modelling of noncatalytic gas-solid reactions is introduced with particular emphasis on char gasification. A Bethe network description of the pore space topology is developed and justified. This approach provides a natural framework for modelling pore opening, enlargement and coalescence in the evolution of porosity and internal accessible surface area with solid conversion. In addition, the description includes the role of pore topology in the particle disintegration at high conversions. Because of the detailed treatment of basic topological features of the internal pore structure, the model is able to predict experimental observations for a variety of conditions.

A model for gas-solid reactions with structural changes in the presence of inert solids

A mathematical model is developed to account for the effect of inert material present in the solid in noncatalytic gas-solid reactions accompanied by significant structural changes. This model finds application in the desulfurization of flue gases using dolomite, chlorination of ilmenite, etc. where the naturally occurring ores contain inert materials in the solid matrix. The results show that the asymptotic conversion is increased by the presence of inerts and an optimum inert content exists for which the gas uptake and the utilization of the active solid material are maximum.

Self-inhibited rate in gas-solid noncatalytic reactions. The shrinking core model

Self-inhibited rate in gas-solid noncatalytic reactions. The shrinking core model

Simplified solution technique for moving boundary problems in gas-solid non-catalytic reactions

Simplified solution technique for moving boundary problems in gas-solid non-catalytic reactions

Self-inhibited rate in gas-solid noncatalytic reactions: the "rotten apple" phenomenon and multiple reaction pathways

Self-inhibited rate in gas-solid noncatalytic reactions: the "rotten apple" phenomenon and multiple reaction pathways

Analytical prediction of conversion-time behaviour of gas-solid noncatalytic reactions

A procedure has been suggested for analytical prediction of conversion-time behaviour of gas-solid non-catalytic reactions which are first order with respect to the gaseous reactant but of any general form with respect to the solid species. Based on this method analytical solutions have been presente for some of the commonly encountered rate forms including the grain model. These solutions predict the behaviour of the system extremely well upto abou 50–70% conversion of the solid.

Simple conversion relationships for noncatalytic gas-solid reactions. Reply to comments

Simple conversion relationships for noncatalytic gas-solid reactions. Reply to comments

Simple conversion relations for noncatalytic gas-solid reaction. Comments

Simple conversion relations for noncatalytic gas-solid reaction. Comments

On the validity of the shrinking core model in noncatalytic gas solid reaction

By using a matched asymptotic expansion technique, the shrinking core model (SCM) used in non-catalytic gas solid reactions with general kinetic expression is rigorously justified in this paper as a special case of the homogeneous model when the reaction rate is much faster than that of diffusion. The time-pendent velocity of the moving reacted-unreacted interface is found to be proportional to the gas flux at that interface for all geometries of solid particles, and the thickness order of the reaction zone and also the degree of chemical reaction at the interface is discussed in this paper.

Solution of models for gassolid noncatalytic reactions by orthogonal collocation on finite elements with moving boundary

A variable size grain model is used to describe gassolid non-catalytic reactions which are accompanied by change in solid structure. A finite element collocation method with a moving boundary is developed to describe gas and solid concentration profiles in the reacting pellet and to compute conversion-time relationships. Such a method is necessary in case of structural changes which lead to complete pore mouth blockage and gives good results until such blockage occurs. A modified shrinking core model is used as an approximation after the time at which complete pore mouth closure occurs. The developed computational algorithms show that the effect of structural changes on time-conversion relationship is significant.

A variable size grain model for gas-solid reactions with structural changes

The gas-solid noncatalytic reaction of an isothermal pellet is described by a variable-size-grain model and the shrinking core model is used to represe

Analytical prediction of conversion-time behaviour of gas-solid non-catalytic reactions

Analytical prediction of conversion-time behaviour of gas-solid non-catalytic reactions

An experimental reactor for kinetic studies: continuously-fed batch reactor

The use of a continuously-fed batch reacter (CFBR) as an experimental tool for the kinetic studies is presented for liquid- and gas-phase reactions, and noncatalytic gas-solid reactions. An experimental CFBR run is demonstrated using the reaction involving sucrose conversion to substantiate the theoretical results. The concept used for the CFBR is the fact that at an extremum of concentration the rate of concentration change is zero. For the liquid- and gas-phase reactions, the CFBR can be used as an alternative to the CSTR. For slow reactions, the rate determined from a CFBR run is more accurate than the rate determined from a CSTR run. Determination of the rates over the entire conversion range is made easy for fast reactions with the use of the CFBR. Results are extended to noncatalytic gas-solid reactions. It is shown that the fractional change of reacting surface area of the solid reactant can be obtained using the CFBR under the limiting condition of negligible effect of mass transfer.