Reacting porous solids with phase segregation

Melchiori, Tommaso; Gallucci, Fausto; Annaland, Martin van Sint; Canu, Paolo

doi:10.1016/j.ces.2015.04.029

Cited by 6 publications

(8 citation statements)

References 40 publications

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“…The main problem when operating a packed bed is that the oxygen carrier will experience cycles between complete oxidation to complete reduction. In many cases, at high conversion, a sudden decrease in reaction rate occurs that cannot be predicted by simplified models . The model we used herein was not able to predict the experimental conversion versus time curves when a constant diffusion coefficient for a certain temperature was assumed.…”

Section: Test Proceduresmentioning

confidence: 95%

“…In many cases,a th igh conversion, as udden decrease in reaction rate occurs that cannot be predicted by simplified models. [24] Them odel we used herein was not able to predictt he experimental conversion versus time curves when ac onstant diffusion coefficient for ac ertain temperature was assumed.T he change in diffusivity during the reaction must be caused by structural/morphological changes in the particle,a sa lso studied by Szeleky and Propster. [25] Because the determination of the changei n the effective diffusion coefficient is out of the scope of this work, as impled ependency of D on the solid conversion was assumed,a sa lso used previously to describe other gas-solid reactions, [26,27] and also other oxygen-carrier reduction and oxidationr eactions.…”

Section: Kinetic Modelmentioning

confidence: 99%

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Kinetics of the Reactions Prevailing during Packed‐Bed Chemical Looping Combustion of Syngas using Ilmenite

et al. 2016

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Chemical looping combustion has been identified as a very promising technology for power production with integrated carbon dioxide capture. The objective of this work is to study the kinetics of all reactions that are important in the combustion of syngas in a packed‐bed chemical looping reactor by using ilmenite as an oxygen carrier. The reaction kinetics of reduction, with hydrogen and carbon monoxide, and oxidation, with oxygen, of ilmenite‐based pellets have been determined in a thermogravimetric analyzer. The shrinking core model for a spherical geometry was used to obtain the kinetic parameters by considering mixed control by chemical reactions and diffusion through the product layer for all reaction involved. The reduction rate of ilmenite by hydrogen was at least an order of magnitude higher than that by carbon monoxide (especially at higher particle conversions) and the activation energies were found to be 45 and 30 kJ mol−1 for reduction with hydrogen and carbon monoxide, respectively. For the oxidation reaction, a much lower apparent activation energy of 5 kJ mol−1 was found, which indicated that the temperature did not have an important effect on the oxidation kinetics of ilmenite. In addition, the catalytic activity of ilmenite for water gas shift (WGS) was measured in a micro fixed‐bed reactor. An empirical power‐law model was used to describe the kinetics of the WGS reaction over ilmenite.

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Section: Test Proceduresmentioning

confidence: 95%

Section: Kinetic Modelmentioning

confidence: 99%

Kinetics of the Reactions Prevailing during Packed‐Bed Chemical Looping Combustion of Syngas using Ilmenite

et al. 2016

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“…Blamey et al 17 developed a shrinking core model for the description of the hydration reaction of CaO, in which the nonequimolar counterdiffusion has been taken into account, and they found that the decrease of particle porosity and the transition from gaseous diffusion to solid-state diffusion may result in overprediction occurring at higher conversions. Melchiori et al 18 proposed a continuous model in which the solid particle is treated to be consisting of different solid species with a nonuniformly distributed initial composition along its radius and the reduction process may involve multiple reactions. The model has been used to describe the reduction of iron−titanium oxide mineral.…”

Section: Introductionmentioning

confidence: 99%

An Improved Form of Shrinking Core Model for Prediction of the Conversion during Reduction Process in Chemical Looping Combustion

Chen¹,

Yang²,

Li³

et al. 2017

Energy Fuels

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The chemical looping combustion (CLC) process involves the combustion of gaseous fuel through heterogeneous chemical reaction with the oxygen carriers, usually granular metal oxides, in the fluidized bed fuel reactor. It has been recognized that the reaction kinetics of granular metal oxide in the fuel reactor affects the gas−solid flow behavior significantly. This work explores the improvement in one of the most widely adopted kinetic models describing the reduction kinetics, the "chemical control shrinking core model", in which oxide oxygen carriers are assumed to consist of spherical particles. In the analysis, the effects of gas diffusion in the product layer and geometrical irregularity of the oxygen carrier particles on the reaction kinetics are negligible. The work presented in this paper attempts to account for the effects of the gaseous reactant diffusion and particle shape on reaction kinetics by modifying the kinetic model so as to achieve better prediction of the conversion rate in the reduction for the oxygen carriers. The nondimensional form of the derived kinetic model is also discussed. A semiempirical relation is proposed to account for the effect of diffusion changes on the conversion during the reaction. The modeling results have clearly shown that inclusion of the gas diffusion in porous particles can provide better prediction of the reaction kinetics, especially the time for the complete conversion. The shape factor also has a noticeable influence on the conversion rate of oxygen carriers and the time for complete conversion.

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“…An Arrhenius law or higher order kinetic rates could be used if these are more appropriate for the particular application. Melchiori and colleagues [18,19] use a general power P \alpha A in their continuum model, and we comment on this in section 7.4. At the moving reaction interface r = l(t), we have the following conditions, which have been determined by considering the mass flux relative to the interface for A and then B and using (3):…”

mentioning

confidence: 99%

“…A need to capture interactions between smaller granular and larger particle scales leads us to utilize homogenization theory. models [18,19] have been formed to represent such a situation. However, we use the mathematical technique of homogenization to systematically derive models, which can then be compared to those previously studied.…”

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Homogenization of a Shrinking Core Model for Gas–Solid Reactions in Granular Particles

Sloman¹,

Please²,

Gorder³

2019

SIAM J. Appl. Math.

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\bfA \bfb \bfs \bft \bfr \bfa \bfc \bft . Reactions between gases and solid particles are commonly modeled using a shrinking core framework, where a sharp interface between an inner unreacted core and an outer product shell moves inward until the reaction is complete. However, for some physical systems this sharp divide is not present, and so a better model is needed to capture a transition region for the reaction. We are interested in large particles made of many small grains where there are strong interactions between microscale granular and macroscale particulate effects, and where a shrinking core model represents behavior at the microscale level. We obtain homogenized equations for macroscale behavior by exploiting the small ratio of granular to particle lengthscales. These macroscale equations allow for a diffuse reaction front, as well as a sharp interface between reacted and unreacted solid material. We analyze the resulting model asymptotically in the limits where the reaction time is rate-limited by chemical kinetics, and separately by diffusion, determining the thickness of the reaction front. Numerical simulations support the law of additive reaction times, which states that the total reaction time is given as the sum of the conversion times under these limits. We further show how the model results can be extended to incorporate the transport of the product gas out of the solid particle, using a binary Fickian diffusion model. In metallurgical production the particle size and porosity are known to influence reaction times. Our results help quantify these effects and may be an aid in raw material selection.\bfK \bfe \bfy \bfw \bfo \bfr \bfd \bfs . homogenization, gas-solid reactions, porous media, shrinking core model, diffusion, asymptotics \bfA \bfM \bfS \bfs \bfu \bfb \bfj \bfe \bfc \bft \bfc \bfl \bfa \bfs \bfs \bfi fi\bfc \bfa \bft \bfi \bfo \bfn \bfs . 35B27, 35C20, 80A30, 92E20 \bfD \bfO \bfI .

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Reacting porous solids with phase segregation

Cited by 6 publications

References 40 publications

Kinetics of the Reactions Prevailing during Packed‐Bed Chemical Looping Combustion of Syngas using Ilmenite

Kinetics of the Reactions Prevailing during Packed‐Bed Chemical Looping Combustion of Syngas using Ilmenite

An Improved Form of Shrinking Core Model for Prediction of the Conversion during Reduction Process in Chemical Looping Combustion

Homogenization of a Shrinking Core Model for Gas–Solid Reactions in Granular Particles

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