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Effect of perforated ratios of distributor on the fluidization characteristics in a gas-solid fluidized bed / Shuqin Dong in Industrial & engineering chemistry research, Vol. 48 N°1 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 517-527 Titre : Effect of perforated ratios of distributor on the fluidization characteristics in a gas-solid fluidized bed Type de document : texte imprimé Auteurs : Shuqin Dong, Editeur scientifique ; Changqing Cao, Editeur scientifique ; Chongdian Si, Editeur scientifique Année de publication : 2009 Article en page(s) : P. 517-527 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Gas−Solid  Fluid  dynamics Résumé : A gas−solid fluidized bed, 0.14 m in diameter and 1.6 m in height, was employed to investigate systematically the effects of perforated ratios of distributor on fluidization characteristics with air as gas phase and fluid catalytic cracking particles as solid phase. The distributions of the distributor pressure drop, solid particle concentration, and bed pressure drop were obtained by means of different perforated ratios of distributors. The particle concentration distribution and bed pressure drop were measured by a PV-6A particles velocity measurer and a U-manometer, respectively. The parameters of bed pressure drop, distributor pressure drop, the instantaneous evolution of bubbles, and profile of radial solid holdups adopted three perforated ratios of distributors were simulated using computational fluid dynamics code Fluent 6.2. The results showed that the distributor pressure drop decreased with increasing perforated ratios and decreasing superficial gas velocity. The global solid holdup decreased from the wall to center region, and it had parabolic concentration profile under pressure-driven force for different perforated ratios of three distributors investigated. However, the distribution of radial solid holdup was more homogeneous, and it had a better agreement with experiment values for perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributors. The bubble size at the region of distributor decreased with increasing perforated ratio of distributors, and it had more obvious circulation motion of solid particles for the perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributor. The bed pressure drop and root mean square (rms) of bed pressure drop in gas−solid fluidized bed appeared differently for three perforated ratios of distributors. The rms of bed pressure drop for the perforated ratio 0.46% of distributor was larger than that for perforated ratio 0.86 or 1.10% of distributors, and the larger discrepancy occurred as the perforated ratio of distributor was 0.46%. The numerical simulation results agreed well with the experimental data at low superficial gas velocity for calculation of distributor pressure drop. However, larger error occurred at high superficial gas velocity. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801073r [article] Effect of perforated ratios of distributor on the fluidization characteristics in a gas-solid fluidized bed [texte imprimé] / Shuqin Dong, Editeur scientifique ; Changqing Cao, Editeur scientifique ; Chongdian Si, Editeur scientifique . - 2009 . - P. 517-527. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 517-527 Mots-clés : Gas−Solid  Fluid  dynamics Résumé : A gas−solid fluidized bed, 0.14 m in diameter and 1.6 m in height, was employed to investigate systematically the effects of perforated ratios of distributor on fluidization characteristics with air as gas phase and fluid catalytic cracking particles as solid phase. The distributions of the distributor pressure drop, solid particle concentration, and bed pressure drop were obtained by means of different perforated ratios of distributors. The particle concentration distribution and bed pressure drop were measured by a PV-6A particles velocity measurer and a U-manometer, respectively. The parameters of bed pressure drop, distributor pressure drop, the instantaneous evolution of bubbles, and profile of radial solid holdups adopted three perforated ratios of distributors were simulated using computational fluid dynamics code Fluent 6.2. The results showed that the distributor pressure drop decreased with increasing perforated ratios and decreasing superficial gas velocity. The global solid holdup decreased from the wall to center region, and it had parabolic concentration profile under pressure-driven force for different perforated ratios of three distributors investigated. However, the distribution of radial solid holdup was more homogeneous, and it had a better agreement with experiment values for perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributors. The bubble size at the region of distributor decreased with increasing perforated ratio of distributors, and it had more obvious circulation motion of solid particles for the perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributor. The bed pressure drop and root mean square (rms) of bed pressure drop in gas−solid fluidized bed appeared differently for three perforated ratios of distributors. The rms of bed pressure drop for the perforated ratio 0.46% of distributor was larger than that for perforated ratio 0.86 or 1.10% of distributors, and the larger discrepancy occurred as the perforated ratio of distributor was 0.46%. The numerical simulation results agreed well with the experimental data at low superficial gas velocity for calculation of distributor pressure drop. However, larger error occurred at high superficial gas velocity. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801073r

Hydrodynamics and axial dispersion in a gas−liquid−(solid) EL-ALR with different sparger designs / Changqing Cao in Industrial & engineering chemistry research, Vol. 47 n°11 (Juin 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°11 (Juin 2008) . - p. 4008–4017 Titre : Hydrodynamics and axial dispersion in a gas−liquid−(solid) EL-ALR with different sparger designs Type de document : texte imprimé Auteurs : Changqing Cao, Auteur ; Shuqin Dong, Auteur ; Qijin Geng, Auteur ; Qingjie Guo, Auteur Année de publication : 2008 Article en page(s) : p. 4008–4017 Note générale : Bibliogr. p. 4017 Langues : Anglais (eng) Mots-clés : Gs−liquid−(solid);  External-loop  airlift  reactor Résumé : The gas−liquid−(solid) three-phase hydrodynamics in an external-loop airlift reactor (EL-ALR) with an upward pipe 0.47 m in diameter and 2.5 m in height, two external loop downward pipes 0.08 m in diameter and 2.5 m in height, were investigated using four different gas sparger designs. The microconductivity probe and the three-dimensional (3-D) laser Doppler anemometry (LDA) techniques were, respectively, implemented to measure the local gas holdup in the riser (αGr) and liquid phase velocity in the downcomer (ULd) using air as the gas phase, water as the liquid phase, and alginate gel beads as the solid phase, over a wide range of operation conditions. The tracer age distribution was measured using the pulse-pursuit response technology. Axial dispersion model (ADM) was used to estimate the model parameter Peclet number (Pe) values as a fitted parameter with the measured data, using the gold partition method for nonlinear programming strategy inequation restrict conditions. The ADM gave better fits to the experimental data at high axial locations and lower superficial gas velocity (UG) for an EL-ALR used with a large L/DR ratio. A synergistic effect of ULd, αGr, Pe, solids loading (SL), and sparger designs on the performance of an EL-ALR was observed in our experiments. The sparger designs were determined to have a noticeable effect on the αGr and Pe in the lower gas velocity and lower solid loading ranges (UG < 0.025 m/s and SL < 2%), but only a slight effect in the high gas velocity and high solid loading ranges (UG > 0.030 m/s and SL > 3%). However, the effect of sparger designs on the ULd is greater in the gas velocity from 0.025 m/s to 0.045 m/s. For the lower solids loading, the increase of orifice diameter leads to a decrease in αGr. This is in accordance with what was presented in the gas−liquid two-phase system. Moreover, the influence of orifice diameters of the spargers is negligible for solids loading of >3%. Although the Pe values decreased with the operating gas velocity, the gas velocity change from 0.03 m/s to 0.04 m/s yielded lower Pe values, as a result of the reduced bubble size. As the gas velocity further increased to 0.06 m/s, the αGr and the ULd values increased, while the Pe values negligibly increased. For a gas−liquid two-phase system, Pe decreases with the orifice diameter and, for 1% of solids, Pe is also lower for sparger P-2 (ϕ 0.6 mm) than for sparger P-1 (ϕ 0.3 mm). For higher amounts of solids (3%), Pe does not have a defined trend. In addition to the gas velocity and sparger design effects, the solids loading had the effect of decreasing the ULd values, while such effect became small and flattened at high solid loadings. The ULd values, especially with VO = 100%, are ~20% lower in three-phase flow than that in two-phase flow. In addition, the ULd profiles in three-phase flow are flatter than that in two-phase flow with VO = 50%−100%, actually showing a parabolic shape rather than the almost linear one encountered in two-phase flow. This is very important for design and optimum operation that are used to systemically investigate the synergistic effect of ULd, αGr, Pe, solid loading (SL), and sparger designs on hydrodynamic performance of an EL-ALR. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0715254 [article] Hydrodynamics and axial dispersion in a gas−liquid−(solid) EL-ALR with different sparger designs [texte imprimé] / Changqing Cao, Auteur ; Shuqin Dong, Auteur ; Qijin Geng, Auteur ; Qingjie Guo, Auteur . - 2008 . - p. 4008–4017. Bibliogr. p. 4017 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°11 (Juin 2008) . - p. 4008–4017 Mots-clés : Gs−liquid−(solid);  External-loop  airlift  reactor Résumé : The gas−liquid−(solid) three-phase hydrodynamics in an external-loop airlift reactor (EL-ALR) with an upward pipe 0.47 m in diameter and 2.5 m in height, two external loop downward pipes 0.08 m in diameter and 2.5 m in height, were investigated using four different gas sparger designs. The microconductivity probe and the three-dimensional (3-D) laser Doppler anemometry (LDA) techniques were, respectively, implemented to measure the local gas holdup in the riser (αGr) and liquid phase velocity in the downcomer (ULd) using air as the gas phase, water as the liquid phase, and alginate gel beads as the solid phase, over a wide range of operation conditions. The tracer age distribution was measured using the pulse-pursuit response technology. Axial dispersion model (ADM) was used to estimate the model parameter Peclet number (Pe) values as a fitted parameter with the measured data, using the gold partition method for nonlinear programming strategy inequation restrict conditions. The ADM gave better fits to the experimental data at high axial locations and lower superficial gas velocity (UG) for an EL-ALR used with a large L/DR ratio. A synergistic effect of ULd, αGr, Pe, solids loading (SL), and sparger designs on the performance of an EL-ALR was observed in our experiments. The sparger designs were determined to have a noticeable effect on the αGr and Pe in the lower gas velocity and lower solid loading ranges (UG < 0.025 m/s and SL < 2%), but only a slight effect in the high gas velocity and high solid loading ranges (UG > 0.030 m/s and SL > 3%). However, the effect of sparger designs on the ULd is greater in the gas velocity from 0.025 m/s to 0.045 m/s. For the lower solids loading, the increase of orifice diameter leads to a decrease in αGr. This is in accordance with what was presented in the gas−liquid two-phase system. Moreover, the influence of orifice diameters of the spargers is negligible for solids loading of >3%. Although the Pe values decreased with the operating gas velocity, the gas velocity change from 0.03 m/s to 0.04 m/s yielded lower Pe values, as a result of the reduced bubble size. As the gas velocity further increased to 0.06 m/s, the αGr and the ULd values increased, while the Pe values negligibly increased. For a gas−liquid two-phase system, Pe decreases with the orifice diameter and, for 1% of solids, Pe is also lower for sparger P-2 (ϕ 0.6 mm) than for sparger P-1 (ϕ 0.3 mm). For higher amounts of solids (3%), Pe does not have a defined trend. In addition to the gas velocity and sparger design effects, the solids loading had the effect of decreasing the ULd values, while such effect became small and flattened at high solid loadings. The ULd values, especially with VO = 100%, are ~20% lower in three-phase flow than that in two-phase flow. In addition, the ULd profiles in three-phase flow are flatter than that in two-phase flow with VO = 50%−100%, actually showing a parabolic shape rather than the almost linear one encountered in two-phase flow. This is very important for design and optimum operation that are used to systemically investigate the synergistic effect of ULd, αGr, Pe, solid loading (SL), and sparger designs on hydrodynamic performance of an EL-ALR. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0715254

Investigation into bubble size distribution and transient evolution in the sparger region of gas-liquid external loop airlift reactors / Changqing Cao in Industrial & engineering chemistry research, Vol. 48 N° 12 (Juin 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 12 (Juin 2009) . - pp. 5824–5832 Titre : Investigation into bubble size distribution and transient evolution in the sparger region of gas-liquid external loop airlift reactors Type de document : texte imprimé Auteurs : Changqing Cao, Auteur ; Liangliang Zhao, Auteur ; Dongyan Xu, Auteur Année de publication : 2009 Article en page(s) : pp. 5824–5832 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Gas  sparger  Bubble  size  distribution  Gas-liquid  external  loop  airlift  reactors Résumé : It is well-known that the gas sparger can play an important role on the transient evolution of bubbles and bubble size distribution (BSD) in gas−liquid external loop airlift reactors (EL-ALRs). Therefore, the main subject of the present work was to study the influence of sparger design and process parameters on the transient evolution of bubbles and bubble size distribution (BSD) in the sparger region of the considered EL-ALRs. For this purpose, both detailed measurements and prediction of the size of bubbles produced at the sparger were carried out in EL-ALRs with different size and sparger structure parameters. The unique set of BSD curves were obtained by analyzing a large amount of bubbles with a measurement based on an image analysis technique. Additionally, Colella’s model of BSD evolution in bubble columns was further developed by implementing a detailed physical model for predicting the initial BSD at the sparger applied to gas−liquid EL-ALRs where the model input is only based on design/process parameters. A validation of the model was carried out using data from gas−liquid EL-ALRs with different size and sparger design parameters. In order to provide more deep insight for transient evolution of bubbles at the local scale in the sparger region, the computational fluid dynamics (CFD) code Fluent 6.2 was used. The transient evolution of bubbles was simulated in the sparger region of gas−liquid EL-ALR. The simulating results of bubble size are in good agreement at the lower gas velocity with the experimental data in the sparger regions of TU-A and TU-B. With increasing gas flow rate, the difference between simulations and experimental values for bubble size increases. The simulations underestimate bubble size at high gas flow rate. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801700s [article] Investigation into bubble size distribution and transient evolution in the sparger region of gas-liquid external loop airlift reactors [texte imprimé] / Changqing Cao, Auteur ; Liangliang Zhao, Auteur ; Dongyan Xu, Auteur . - 2009 . - pp. 5824–5832. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 12 (Juin 2009) . - pp. 5824–5832 Mots-clés : Gas  sparger  Bubble  size  distribution  Gas-liquid  external  loop  airlift  reactors Résumé : It is well-known that the gas sparger can play an important role on the transient evolution of bubbles and bubble size distribution (BSD) in gas−liquid external loop airlift reactors (EL-ALRs). Therefore, the main subject of the present work was to study the influence of sparger design and process parameters on the transient evolution of bubbles and bubble size distribution (BSD) in the sparger region of the considered EL-ALRs. For this purpose, both detailed measurements and prediction of the size of bubbles produced at the sparger were carried out in EL-ALRs with different size and sparger structure parameters. The unique set of BSD curves were obtained by analyzing a large amount of bubbles with a measurement based on an image analysis technique. Additionally, Colella’s model of BSD evolution in bubble columns was further developed by implementing a detailed physical model for predicting the initial BSD at the sparger applied to gas−liquid EL-ALRs where the model input is only based on design/process parameters. A validation of the model was carried out using data from gas−liquid EL-ALRs with different size and sparger design parameters. In order to provide more deep insight for transient evolution of bubbles at the local scale in the sparger region, the computational fluid dynamics (CFD) code Fluent 6.2 was used. The transient evolution of bubbles was simulated in the sparger region of gas−liquid EL-ALR. The simulating results of bubble size are in good agreement at the lower gas velocity with the experimental data in the sparger regions of TU-A and TU-B. With increasing gas flow rate, the difference between simulations and experimental values for bubble size increases. The simulations underestimate bubble size at high gas flow rate. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801700s

Investigation into photocatalytic degradation of gaseous ammonia in CPCR / Qijin Geng in Industrial & engineering chemistry research, Vol. 47 N° 13 (Juillet 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4363–4368 Titre : Investigation into photocatalytic degradation of gaseous ammonia in CPCR Type de document : texte imprimé Auteurs : Qijin Geng, Auteur ; Qingjie Guo, Auteur ; Changqing Cao, Auteur ; Yunchen Zhang, Auteur Année de publication : 2008 Article en page(s) : p. 4363–4368 Note générale : Bibliogr. p. 4368 Langues : Anglais (eng) Mots-clés : Ammonia;  Circulated  photocatalytic  reactor;  Photocatalytic  degradation Résumé : Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution because of continuous transformation and emission of urea to gaseous ammonia on indoor concrete walls. To control ammonia pollution from indoor concrete walls, a circulated photocatalytic reactor (CPCR) was designed to intensify the performance for the decomposition of gaseous ammonia in the present study and TiO2 film photocatalysts were prepared by the sol−gel method and coating onto the inner wall of this reactor using a bonder of polyacrylic ester emulsion, which was characterized by FTIR, TEM, and SEM. In particular, the influences of initial concentration of ammonia on the degradation conversion (Dp), apparent reaction rate constants (kr), initial degradation rate (r), deactivation, and regeneration of catalyst in CPCR were investigated. Furthermore, a designed equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in CPCR. The total number of adsorption sites available for the gas molecules NT and the adsorption equilibrium constant Kads values were determined through a linear-fitting method. Finally, undesirable NO2− and NO3− were detected as the intermediates in the process of photodegradation at different initial concentration of ammonia, which was detected by catalytic kinetic spectrophotometry. The results indicated that the degradation conversion (Dp), initial degradation rate (r), degraded products, and half-life (t1/2) were closely correlated to the initial concentration of ammonia. It was found that the reaction kinetics fixed the pseudofirst-order kinetic equation of photocatalytic degradation of gaseous ammonia in CPCR, and the kinetic results are discussed in terms of adsorption of ammonia and products degraded. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800274g [article] Investigation into photocatalytic degradation of gaseous ammonia in CPCR [texte imprimé] / Qijin Geng, Auteur ; Qingjie Guo, Auteur ; Changqing Cao, Auteur ; Yunchen Zhang, Auteur . - 2008 . - p. 4363–4368. Bibliogr. p. 4368 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4363–4368 Mots-clés : Ammonia;  Circulated  photocatalytic  reactor;  Photocatalytic  degradation Résumé : Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution because of continuous transformation and emission of urea to gaseous ammonia on indoor concrete walls. To control ammonia pollution from indoor concrete walls, a circulated photocatalytic reactor (CPCR) was designed to intensify the performance for the decomposition of gaseous ammonia in the present study and TiO2 film photocatalysts were prepared by the sol−gel method and coating onto the inner wall of this reactor using a bonder of polyacrylic ester emulsion, which was characterized by FTIR, TEM, and SEM. In particular, the influences of initial concentration of ammonia on the degradation conversion (Dp), apparent reaction rate constants (kr), initial degradation rate (r), deactivation, and regeneration of catalyst in CPCR were investigated. Furthermore, a designed equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in CPCR. The total number of adsorption sites available for the gas molecules NT and the adsorption equilibrium constant Kads values were determined through a linear-fitting method. Finally, undesirable NO2− and NO3− were detected as the intermediates in the process of photodegradation at different initial concentration of ammonia, which was detected by catalytic kinetic spectrophotometry. The results indicated that the degradation conversion (Dp), initial degradation rate (r), degraded products, and half-life (t1/2) were closely correlated to the initial concentration of ammonia. It was found that the reaction kinetics fixed the pseudofirst-order kinetic equation of photocatalytic degradation of gaseous ammonia in CPCR, and the kinetic results are discussed in terms of adsorption of ammonia and products degraded. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800274g