Documents disponibles écrits par cet auteur

Dynamics of axially dispersed reactors / Li, Mingheng in Industrial & engineering chemistry research, Vol. 47 n°14 (Juillet 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°14 (Juillet 2008) . - p. 4797–4806 Titre : Dynamics of axially dispersed reactors Type de document : texte imprimé Auteurs : Li, Mingheng, Auteur Année de publication : 2008 Article en page(s) : p. 4797–4806 Langues : Anglais (eng) Mots-clés : Axially  dispersed  reactors;  State-space  approach;  Proper  orthogonal  decomposition  technique Résumé : Axially dispersed reactors with simultaneous convection, dispersion, and reaction might be used to approximate real reactors. While the steady-state solution to an axially dispersed reactor is well-described in the literature, its dynamic behavior is not often discussed. Studying this problem could provide insights into a class of industrial concentration transition problems, such as the product change in a glass melting furnace where one glass product is gradually replaced by another with a different composition. In this work, the dynamics in a tubular reactor with significant axial dispersion are explored following a state-space approach. The state-space models can be constructed either analytically or numerically. In the analytical approach, a continuous-time state-space model is derived from eigenfunction expansion followed by solving a Sturm−Liouville problem. In the numerical approach, a high-dimensional discrete-time state-space model is formulated by the discretization of the process PDE using the implicit finite-difference scheme. The proper orthogonal decomposition (POD) technique is then used to reduce the order of the state-space model. In either case, an optimal trajectory of the feed composition with bounded constraints to achieve a transition in the outlet concentration is solved based on the reduced models using quadratic programming. Computer simulations are used to demonstrate that substantial dispersions, if they exist in a reactor, can significantly affect the reactor dynamics (i.e., a long time might be required to make a concentration transition). In such a case, an optimal feed trajectory solved by dynamic optimization can be used to significantly reduce the transition time. Potential applications to the glass product transition are discussed. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800083e [article] Dynamics of axially dispersed reactors [texte imprimé] / Li, Mingheng, Auteur . - 2008 . - p. 4797–4806. Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°14 (Juillet 2008) . - p. 4797–4806 Mots-clés : Axially  dispersed  reactors;  State-space  approach;  Proper  orthogonal  decomposition  technique Résumé : Axially dispersed reactors with simultaneous convection, dispersion, and reaction might be used to approximate real reactors. While the steady-state solution to an axially dispersed reactor is well-described in the literature, its dynamic behavior is not often discussed. Studying this problem could provide insights into a class of industrial concentration transition problems, such as the product change in a glass melting furnace where one glass product is gradually replaced by another with a different composition. In this work, the dynamics in a tubular reactor with significant axial dispersion are explored following a state-space approach. The state-space models can be constructed either analytically or numerically. In the analytical approach, a continuous-time state-space model is derived from eigenfunction expansion followed by solving a Sturm−Liouville problem. In the numerical approach, a high-dimensional discrete-time state-space model is formulated by the discretization of the process PDE using the implicit finite-difference scheme. The proper orthogonal decomposition (POD) technique is then used to reduce the order of the state-space model. In either case, an optimal trajectory of the feed composition with bounded constraints to achieve a transition in the outlet concentration is solved based on the reduced models using quadratic programming. Computer simulations are used to demonstrate that substantial dispersions, if they exist in a reactor, can significantly affect the reactor dynamics (i.e., a long time might be required to make a concentration transition). In such a case, an optimal feed trajectory solved by dynamic optimization can be used to significantly reduce the transition time. Potential applications to the glass product transition are discussed. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800083e

Equilibrium calculation of gaseous reactive systems with simultaneous species adsorption / Li, Mingheng in Industrial & engineering chemistry research, Vol. 47 N° 23 (Décembre 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N° 23 (Décembre 2008) . - p. 9263–9271 Titre : Equilibrium calculation of gaseous reactive systems with simultaneous species adsorption Type de document : texte imprimé Auteurs : Li, Mingheng, Auteur Année de publication : 2009 Article en page(s) : p. 9263–9271 Note générale : Chemistry engineering Langues : Anglais (eng) Mots-clés : Gaseous  Reactive  Systems  Species  Adsorption Résumé : This work focuses on the calculation of chemical equilibrium in a gaseous reactive system with simultaneous single or multiple species adsorption under isothermal and isobaric conditions. Two different algorithms are developed, following the minimization of Gibbs free energy and the concept of equilibrium constant, respectively. In either case, the problem formulation is converted to a set of nonlinear algebraic equations that are solved using the Newton−Raphson scheme. An example of steam reforming of ethanol with simultaneous CO2 adsorption is used to illustrate the proposed approaches. It is shown that at T = 500 °C and P = 5 bar, the CO2 removal ratio should exceed 40% to achieve a decent enhancement in hydrogen production and purity. An integrated process that combines the endothermic reforming and the exothermic combustion of CH4 from the off-gas supplemented with simultaneous CO2 adsorption in the reforming process yields a theoretical maximum overall conversion rate of 86.3% (the corresponding H2 purity out of the reformer is 89.4% on a wet basis, or 96.2% on a dry basis) with little or no external heat supply. The analysis in this work is potentially useful in the design and optimization of adsorption-enhanced reforming reactors for hydrogen generation and other applicable reactive systems. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800408m [article] Equilibrium calculation of gaseous reactive systems with simultaneous species adsorption [texte imprimé] / Li, Mingheng, Auteur . - 2009 . - p. 9263–9271. Chemistry engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N° 23 (Décembre 2008) . - p. 9263–9271 Mots-clés : Gaseous  Reactive  Systems  Species  Adsorption Résumé : This work focuses on the calculation of chemical equilibrium in a gaseous reactive system with simultaneous single or multiple species adsorption under isothermal and isobaric conditions. Two different algorithms are developed, following the minimization of Gibbs free energy and the concept of equilibrium constant, respectively. In either case, the problem formulation is converted to a set of nonlinear algebraic equations that are solved using the Newton−Raphson scheme. An example of steam reforming of ethanol with simultaneous CO2 adsorption is used to illustrate the proposed approaches. It is shown that at T = 500 °C and P = 5 bar, the CO2 removal ratio should exceed 40% to achieve a decent enhancement in hydrogen production and purity. An integrated process that combines the endothermic reforming and the exothermic combustion of CH4 from the off-gas supplemented with simultaneous CO2 adsorption in the reforming process yields a theoretical maximum overall conversion rate of 86.3% (the corresponding H2 purity out of the reformer is 89.4% on a wet basis, or 96.2% on a dry basis) with little or no external heat supply. The analysis in this work is potentially useful in the design and optimization of adsorption-enhanced reforming reactors for hydrogen generation and other applicable reactive systems. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800408m

Minimization of Energy in Reverse Osmosis Water Desalination Using Constrained Nonlinear Optimization / Li, Mingheng in Industrial & engineering chemistry research, Vol. 49 N° 4 (Fevrier 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 4 (Fevrier 2010) . - pp 1822–1831 Titre : Minimization of Energy in Reverse Osmosis Water Desalination Using Constrained Nonlinear Optimization Type de document : texte imprimé Auteurs : Li, Mingheng, Auteur Année de publication : 2010 Article en page(s) : pp 1822–1831 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Osmosis  water  desalination  Nonlinear  optimization. Résumé : This work focuses on the minimization of energy in reverse osmosis water desalination. First, a set of dimensionless parameters were derived to characterize the reverse osmosis desalination process. On the basis of the assumptions of constant pump efficiency and no pressure change in the retentate, the minimization of energy cost per volume of produced permeate or specific energy consumption (SEC) for three different reverse osmosis modules (single-stage, two-stage, and single-stage with an energy recovery device (ERD)) were then formulated and solved as constrained nonlinear optimization problems. Without ERD, the optimal solution to SEC normalized by the feed salinity was solely dependent on a dimensionless parameter γ that is comprised of the membrane area, hydraulic permeability, feed rate, and salinity. In the thermodynamic limit where γ approaches infinity, the minimal SEC approaches 4 and 3.596 times the feed salinity and the fractional recovery approaches 0.5 and 0.574 for single-stage and two-stage reverse osmosis modules, respectively. However, the water yield approaches zero in both cases. With an ERD, the SEC can be further reduced to the feed salinity while the fractional recovery approaches zero. It is also shown that the SEC flattens out quickly as γ increases, and a cutoff of γ (around 0.5−1.5 for one-stage and 1−3 for two-stage membrane modules) can be used to achieve a reasonable water yield as well as a low SEC slightly above the theoretical global minimum. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9012826 [article] Minimization of Energy in Reverse Osmosis Water Desalination Using Constrained Nonlinear Optimization [texte imprimé] / Li, Mingheng, Auteur . - 2010 . - pp 1822–1831. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 4 (Fevrier 2010) . - pp 1822–1831 Mots-clés : Osmosis  water  desalination  Nonlinear  optimization. Résumé : This work focuses on the minimization of energy in reverse osmosis water desalination. First, a set of dimensionless parameters were derived to characterize the reverse osmosis desalination process. On the basis of the assumptions of constant pump efficiency and no pressure change in the retentate, the minimization of energy cost per volume of produced permeate or specific energy consumption (SEC) for three different reverse osmosis modules (single-stage, two-stage, and single-stage with an energy recovery device (ERD)) were then formulated and solved as constrained nonlinear optimization problems. Without ERD, the optimal solution to SEC normalized by the feed salinity was solely dependent on a dimensionless parameter γ that is comprised of the membrane area, hydraulic permeability, feed rate, and salinity. In the thermodynamic limit where γ approaches infinity, the minimal SEC approaches 4 and 3.596 times the feed salinity and the fractional recovery approaches 0.5 and 0.574 for single-stage and two-stage reverse osmosis modules, respectively. However, the water yield approaches zero in both cases. With an ERD, the SEC can be further reduced to the feed salinity while the fractional recovery approaches zero. It is also shown that the SEC flattens out quickly as γ increases, and a cutoff of γ (around 0.5−1.5 for one-stage and 1−3 for two-stage membrane modules) can be used to achieve a reasonable water yield as well as a low SEC slightly above the theoretical global minimum. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9012826