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Fuel reformation and hydrogen generation with direct droplet impingement reactors / Mark J. Varady in Industrial & engineering chemistry research, Vol. 50 N° 16 (Août 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9502-9513 Titre : Fuel reformation and hydrogen generation with direct droplet impingement reactors : model formulation and validation Type de document : texte imprimé Auteurs : Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2011 Article en page(s) : pp. 9502-9513 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Modeling  Reactor  Droplet  Hydrogen  production  Fuel Résumé : Onboard fuel reforming to produce hydrogen for portable fuel cell applications has been widely studied because the liquid has a high volumetric density as an energy storage medium. Several portable fuel reforming devices presented in the literature attempt to scale down the designs of traditional large-scale unit operations, an approach that becomes suboptimal as the size of the application is reduced. Unique reactor designs in which the various unit operations are combined in a synergistic manner are required to achieve higher energy densities and more compact reactors. Spraying a finely atomized liquid directly onto a hot catalyst is one such method that has been experimentally demonstrated. This work focuses on developing a fundamental understanding of this approach and optimizing it by utilizing a droplet generator array with precise control over the droplet spating, diameter, velocity, and trajectory, thus providing ultimate control over the reactor performance. The regular nature of the droplet generator array also enables modeling on a reactor-unit-cell basis with minimal empiricism, which can be used to optimize the reactor performance. The steady-state unit-cell model developed in this work accounts for the transport and evaporation of the droplet stream, impingement and subsequent film accumulation and vaporization, and gas-phase transport and reaction. The key components of the model were validated using relevant results from the literature to establish confidence in applying the complete model to predict reactor performance. Further, a reactor prototype mimicking the reactor unit cell used in the simulations was constructed and used to experimentally validate the comprehensive transport-reaction model for the specific case of methanol steam reforming, In a companion article, this complete model was used to study the effects of reactor operating parameters on conversion selectivity, and power density, aiming at an optimal reactor design. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425191 [article] Fuel reformation and hydrogen generation with direct droplet impingement reactors : model formulation and validation [texte imprimé] / Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur . - 2011 . - pp. 9502-9513. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9502-9513 Mots-clés : Modeling  Reactor  Droplet  Hydrogen  production  Fuel Résumé : Onboard fuel reforming to produce hydrogen for portable fuel cell applications has been widely studied because the liquid has a high volumetric density as an energy storage medium. Several portable fuel reforming devices presented in the literature attempt to scale down the designs of traditional large-scale unit operations, an approach that becomes suboptimal as the size of the application is reduced. Unique reactor designs in which the various unit operations are combined in a synergistic manner are required to achieve higher energy densities and more compact reactors. Spraying a finely atomized liquid directly onto a hot catalyst is one such method that has been experimentally demonstrated. This work focuses on developing a fundamental understanding of this approach and optimizing it by utilizing a droplet generator array with precise control over the droplet spating, diameter, velocity, and trajectory, thus providing ultimate control over the reactor performance. The regular nature of the droplet generator array also enables modeling on a reactor-unit-cell basis with minimal empiricism, which can be used to optimize the reactor performance. The steady-state unit-cell model developed in this work accounts for the transport and evaporation of the droplet stream, impingement and subsequent film accumulation and vaporization, and gas-phase transport and reaction. The key components of the model were validated using relevant results from the literature to establish confidence in applying the complete model to predict reactor performance. Further, a reactor prototype mimicking the reactor unit cell used in the simulations was constructed and used to experimentally validate the comprehensive transport-reaction model for the specific case of methanol steam reforming, In a companion article, this complete model was used to study the effects of reactor operating parameters on conversion selectivity, and power density, aiming at an optimal reactor design. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425191

Fuel reformation and hydrogen generation with direct droplet impingement reactors / Mark J. Varady in Industrial & engineering chemistry research, Vol. 50 N° 16 (Août 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9514-9524 Titre : Fuel reformation and hydrogen generation with direct droplet impingement reactors : parametric study and design considerations for portable methanol steam reformers Type de document : texte imprimé Auteurs : Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2011 Article en page(s) : pp. 9514-9524 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Water  vapor  Design  Reactor  Droplet  Hydrogen  production  Fuel Résumé : In a companion article (Varady and Fedorov Ind. Eng. Chem. Res. 2011, DOI: 10.1021/ie200563e), the concept of a direct droplet impingement reactor (DDIR) was introduced as a promising approach to liquid fuel reformation for distributed hydrogen generation. Considering the overall device as an array of unit cells enabled simplified modeling of the device on a unit-cell basis. In this study, the unit-cell model is utilized to study the effects of the important reactor operating parameters for the specific case of methanol steam reforming. The performance of the baseline DDIR is compared to the ideal limit of an isothermal plug-flow reactor (PFR). The effects of DDIR shape, size, heat input and location, and droplet initial conditions were varied from the baseline design to identify possible performance improvements. It was found that the selectivity displays a distinct marimum at a Pedet number (Pe) of ∼3 because of the interplay between back-diffusion of the products and thermal resistance of the catalyst bed. The spatial heating distribution also plays a key role, where an optimized matching of the heat input locations to the areas of heat consumption due to liquid vaporization and endothermic reaction results in an improved reactor performance, albeit at the penalty of a more complex reactor design and increased cost. Impingement of the droplet stream on the catalyst interface is necessary for proper operation, which requires certain initial droplet conditions to be satisfied, as expressed in the form of an operating regime map. Although the results are presented only for methanol steam reforming, the DDIR model is comprehensive and sufficiently general in terms of incorporated physical phenomena that it should be useful for developing similar operating criteria for other fuels and reactions requiring vaporization of a liquid feed followed by reaction over a fixed catalyst bed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425192 [article] Fuel reformation and hydrogen generation with direct droplet impingement reactors : parametric study and design considerations for portable methanol steam reformers [texte imprimé] / Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur . - 2011 . - pp. 9514-9524. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9514-9524 Mots-clés : Water  vapor  Design  Reactor  Droplet  Hydrogen  production  Fuel Résumé : In a companion article (Varady and Fedorov Ind. Eng. Chem. Res. 2011, DOI: 10.1021/ie200563e), the concept of a direct droplet impingement reactor (DDIR) was introduced as a promising approach to liquid fuel reformation for distributed hydrogen generation. Considering the overall device as an array of unit cells enabled simplified modeling of the device on a unit-cell basis. In this study, the unit-cell model is utilized to study the effects of the important reactor operating parameters for the specific case of methanol steam reforming. The performance of the baseline DDIR is compared to the ideal limit of an isothermal plug-flow reactor (PFR). The effects of DDIR shape, size, heat input and location, and droplet initial conditions were varied from the baseline design to identify possible performance improvements. It was found that the selectivity displays a distinct marimum at a Pedet number (Pe) of ∼3 because of the interplay between back-diffusion of the products and thermal resistance of the catalyst bed. The spatial heating distribution also plays a key role, where an optimized matching of the heat input locations to the areas of heat consumption due to liquid vaporization and endothermic reaction results in an improved reactor performance, albeit at the penalty of a more complex reactor design and increased cost. Impingement of the droplet stream on the catalyst interface is necessary for proper operation, which requires certain initial droplet conditions to be satisfied, as expressed in the form of an operating regime map. Although the results are presented only for methanol steam reforming, the DDIR model is comprehensive and sufficiently general in terms of incorporated physical phenomena that it should be useful for developing similar operating criteria for other fuels and reactions requiring vaporization of a liquid feed followed by reaction over a fixed catalyst bed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425192