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Effect of particle porosity on hysteresis in trickle-bed reactors / rabindranath Maiti in Industrial & engineering chemistry research, Vol. 47 n°21 (Novembre 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°21 (Novembre 2008) . - p. 8126–8135 Titre : Effect of particle porosity on hysteresis in trickle-bed reactors Type de document : texte imprimé Auteurs : rabindranath Maiti, Auteur ; Arnab Atta, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2008 Article en page(s) : p. 8126–8135 Note générale : chemical engineering Langues : Anglais (eng) Mots-clés : HydrodynamicsParticle  porosity Résumé : Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs. View: PDF | PDF w/ Links | Full Text HTML En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8003539 [article] Effect of particle porosity on hysteresis in trickle-bed reactors [texte imprimé] / rabindranath Maiti, Auteur ; Arnab Atta, Auteur ; K. D. P. Nigam, Auteur . - 2008 . - p. 8126–8135. chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°21 (Novembre 2008) . - p. 8126–8135 Mots-clés : HydrodynamicsParticle  porosity Résumé : Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs. View: PDF | PDF w/ Links | Full Text HTML En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8003539

(Gas)-liquid-solid circulating fluidized bed reactors / Arnab Atta in Industrial & engineering chemistry research, Vol. 48 N° 17 (Septembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 17 (Septembre 2009) . - pp. 7876–7892 Titre : (Gas)-liquid-solid circulating fluidized bed reactors : characteristics and applications Type de document : texte imprimé Auteurs : Arnab Atta, Auteur ; S. A. Razzak, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2009 Article en page(s) : pp. 7876–7892 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Circulating  fluidized  beds  Gas-solid  circulating  fluidized  beds  Gas-liquid-solid  circulating  fluidized  beds Résumé : Accepting considerable advantages of circulating fluidized beds (CFBs) over the conventional fluidized beds, there has been numerous studies on CFBs concentrating primarily on the development of gas−solid circulating fluidized beds (GSCFBs). However a substantial amount of research has also been devoted to other two types of CFBs, namely liquid−solid and gas−liquid−solid circulating fluidized beds (LS and GLSCFBs). In this effort, an attempt has been made to summarize and review the research and progresses made on the last two types of CFBs since the highlighting of their hydrodynamics and potential applications in various industries by Zhu et al. [Can. J. Chem. Eng. 2000, 78, 82−94]. The issues associated with its hydrodynamics, scale-up, and design have been discussed with a re-emphasis on its potential application for various cost-effective processes. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900163t [article] (Gas)-liquid-solid circulating fluidized bed reactors : characteristics and applications [texte imprimé] / Arnab Atta, Auteur ; S. A. Razzak, Auteur ; K. D. P. Nigam, Auteur . - 2009 . - pp. 7876–7892. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 17 (Septembre 2009) . - pp. 7876–7892 Mots-clés : Circulating  fluidized  beds  Gas-solid  circulating  fluidized  beds  Gas-liquid-solid  circulating  fluidized  beds Résumé : Accepting considerable advantages of circulating fluidized beds (CFBs) over the conventional fluidized beds, there has been numerous studies on CFBs concentrating primarily on the development of gas−solid circulating fluidized beds (GSCFBs). However a substantial amount of research has also been devoted to other two types of CFBs, namely liquid−solid and gas−liquid−solid circulating fluidized beds (LS and GLSCFBs). In this effort, an attempt has been made to summarize and review the research and progresses made on the last two types of CFBs since the highlighting of their hydrodynamics and potential applications in various industries by Zhu et al. [Can. J. Chem. Eng. 2000, 78, 82−94]. The issues associated with its hydrodynamics, scale-up, and design have been discussed with a re-emphasis on its potential application for various cost-effective processes. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900163t