Documents disponibles écrits par cet auteur

An inexact trust - region algorithm for the optimization of periodic adsorption processes / Sree Rama Raju Vetukuri in Industrial & engineering chemistry research, Vol. 49 N° 23 (Décembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp.12004–12013 Titre : An inexact trust - region algorithm for the optimization of periodic adsorption processes Type de document : texte imprimé Auteurs : Sree Rama Raju Vetukuri, Auteur ; Lorenz T. Biegler, Auteur ; Andrea Walther, Auteur Année de publication : 2011 Article en page(s) : pp.12004–12013 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimization  Adsorption Résumé : Periodic adsorption processes have gained increasing commercial importance as an energy-efficient separation technique over the past two decades. Based on fluid−solid interactions, these systems never reach steady state. Instead they operate at cyclic steady state, where the bed conditions at the beginning of the cycle match with those at the end of the cycle. Nevertheless, optimization of these processes remains particularly challenging, because cyclic operation leads to dense Jacobians, whose computation dominates the overall cost of the optimization strategy. To efficiently handle these Jacobians during optimization and reduce the computation time, this work presents a new composite step trust-region algorithm for the solution of minimization problems with both nonlinear equality and inequality constraints, and combines two approaches developed in Walther(1) and Arora and Biegler.(2) Instead of forming and factoring the dense constraint Jacobian, this algorithm approximates the Jacobian of equality constraints with a specialized quasi-Newton method. Hence it is well suited to solve optimization problems related to periodic adsorption processes. In addition to allowing inexactness of the Jacobian and its null-space representation, the algorithm also provides exact second-order information in the form of Hessian−vector products to improve the convergence rate. The resulting approach(3) also combines automatic differentiation and more sophisticated integration algorithms to evaluate the direct sensitivity and adjoint sensitivity equations. A 5-fold reduction in computation is demonstrated with this approach for two periodic adsorption optimization problems: a simulated moving bed system and a nonisothermal vacuum swing adsorption O2 bulk gas separation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100706c [article] An inexact trust - region algorithm for the optimization of periodic adsorption processes [texte imprimé] / Sree Rama Raju Vetukuri, Auteur ; Lorenz T. Biegler, Auteur ; Andrea Walther, Auteur . - 2011 . - pp.12004–12013. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp.12004–12013 Mots-clés : Optimization  Adsorption Résumé : Periodic adsorption processes have gained increasing commercial importance as an energy-efficient separation technique over the past two decades. Based on fluid−solid interactions, these systems never reach steady state. Instead they operate at cyclic steady state, where the bed conditions at the beginning of the cycle match with those at the end of the cycle. Nevertheless, optimization of these processes remains particularly challenging, because cyclic operation leads to dense Jacobians, whose computation dominates the overall cost of the optimization strategy. To efficiently handle these Jacobians during optimization and reduce the computation time, this work presents a new composite step trust-region algorithm for the solution of minimization problems with both nonlinear equality and inequality constraints, and combines two approaches developed in Walther(1) and Arora and Biegler.(2) Instead of forming and factoring the dense constraint Jacobian, this algorithm approximates the Jacobian of equality constraints with a specialized quasi-Newton method. Hence it is well suited to solve optimization problems related to periodic adsorption processes. In addition to allowing inexactness of the Jacobian and its null-space representation, the algorithm also provides exact second-order information in the form of Hessian−vector products to improve the convergence rate. The resulting approach(3) also combines automatic differentiation and more sophisticated integration algorithms to evaluate the direct sensitivity and adjoint sensitivity equations. A 5-fold reduction in computation is demonstrated with this approach for two periodic adsorption optimization problems: a simulated moving bed system and a nonisothermal vacuum swing adsorption O2 bulk gas separation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100706c

Fast offset-free nonlinear model predictive control based on moving horizon estimation / Rui Huang in Industrial & engineering chemistry research, Vol. 49 N° 17 (Septembre 1, 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 17 (Septembre 1, 2010) . - pp 7882–7890 Titre : Fast offset-free nonlinear model predictive control based on moving horizon estimation Type de document : texte imprimé Auteurs : Rui Huang, Auteur ; Lorenz T. Biegler, Auteur ; Sachin C. Patwardhan, Auteur Année de publication : 2010 Article en page(s) : pp 7882–7890 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Predictive  control  Nonlinear  model. Résumé : To deal with plant−model mismatches in control practice, this paper proposes two variations of an offset-free framework which integrates nonlinear model predictive control (NMPC) and moving horizon estimation (MHE). We prove that the proposed method achieves offset-free regulatory behavior, even in the presence of plant−model mismatches. If the plant uncertainty structure is known, the MHE can be tuned to estimate uncertainty parameters, to remove the plant−model mismatch online. In addition, we incorporate the advanced step NMPC (as-NMPC) and the advanced step MHE (as-MHE) strategies into the proposed method to reduce online computational delay. Finally, the proposed method is applied on a large scale air separation unit, and the steady state offset-free behavior is observed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901945y [article] Fast offset-free nonlinear model predictive control based on moving horizon estimation [texte imprimé] / Rui Huang, Auteur ; Lorenz T. Biegler, Auteur ; Sachin C. Patwardhan, Auteur . - 2010 . - pp 7882–7890. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 17 (Septembre 1, 2010) . - pp 7882–7890 Mots-clés : Predictive  control  Nonlinear  model. Résumé : To deal with plant−model mismatches in control practice, this paper proposes two variations of an offset-free framework which integrates nonlinear model predictive control (NMPC) and moving horizon estimation (MHE). We prove that the proposed method achieves offset-free regulatory behavior, even in the presence of plant−model mismatches. If the plant uncertainty structure is known, the MHE can be tuned to estimate uncertainty parameters, to remove the plant−model mismatch online. In addition, we incorporate the advanced step NMPC (as-NMPC) and the advanced step MHE (as-MHE) strategies into the proposed method to reduce online computational delay. Finally, the proposed method is applied on a large scale air separation unit, and the steady state offset-free behavior is observed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901945y

Superstructure - based optimal synthesis of pressure swing adsorption cycles for precombustion CO2 capture / Agarwal, Anshul in Industrial & engineering chemistry research, Vol. 49 N° 11 (Juin 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 11 (Juin 2010) . - pp. 5066–5079 Titre : Superstructure - based optimal synthesis of pressure swing adsorption cycles for precombustion CO2 capture Type de document : texte imprimé Auteurs : Agarwal, Anshul, Auteur ; Lorenz T. Biegler, Auteur ; Stephen E. Zitney, Auteur Année de publication : 2010 Article en page(s) : pp. 5066–5079 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Adsorption  Precombustion Résumé : Pressure/vacuum swing adsorption (PSA/VSA) technology has been widely applied for H2 production from the effluent streams of a shift converter, which predominantly comprises H2 and CO2 with other trace components. It also offers significant advantages for precombustion CO2 capture in terms of performance, energy requirements, and operating costs since the shifted synthesis gas (syngas) is available for separation at a high pressure with a high CO2 concentration. Most commercial PSA cycles have been developed to recover H2 at very high purity and do not focus on enriching the strongly adsorbed CO2. Thus, a major limitation exists with the use of these conventional PSA cycles for high purity CO2 capture. Furthermore, complex dynamic behavior of PSA processes together with the numerical difficulties of the model governed by partial differential and algebraic equations (PDAEs) makes the evaluation and assessment of different operating steps and cycle configurations difficult and time-consuming. Therefore, a systematic methodology is essential to design and optimize PSA cycles to recover both H2 and CO2 at a high purity. Recent advances in large-scale optimization strategies for process synthesis have enabled us to address this issue with the help of a systematic optimization-based formulation. In particular, we present a superstructure-based approach to simultaneously determine optimal cycle configurations and design parameters for PSA units. The superstructure is capable to predict a rich set of different PSA operating steps, which are accomplished by manipulating the bed connections with the help of time dependent control variables. An optimal sequence of operating steps is achieved through the formulation of an optimal control problem with the PDAEs of the PSA system. Numerical results for case-studies related to precombustion CO2 capture from a shifted syngas feed mixture having hydrogen and carbon dioxide are presented. In particular, optimal PSA cycles are synthesized which maximize CO2 recovery or minimize overall power consumption. The results show the potential of the superstructure to predict PSA cycles with purities as high as 99% for H2 and 96% for CO2. Moreover, these cycles can recover more than 92% of CO2 with a power consumption as low as 46.8 kW h/tonne CO2 captured. The approach presented is therefore quite useful for evaluating the suitability of different operating strategies for PSA processes. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900873j [article] Superstructure - based optimal synthesis of pressure swing adsorption cycles for precombustion CO2 capture [texte imprimé] / Agarwal, Anshul, Auteur ; Lorenz T. Biegler, Auteur ; Stephen E. Zitney, Auteur . - 2010 . - pp. 5066–5079. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 11 (Juin 2010) . - pp. 5066–5079 Mots-clés : Adsorption  Precombustion Résumé : Pressure/vacuum swing adsorption (PSA/VSA) technology has been widely applied for H2 production from the effluent streams of a shift converter, which predominantly comprises H2 and CO2 with other trace components. It also offers significant advantages for precombustion CO2 capture in terms of performance, energy requirements, and operating costs since the shifted synthesis gas (syngas) is available for separation at a high pressure with a high CO2 concentration. Most commercial PSA cycles have been developed to recover H2 at very high purity and do not focus on enriching the strongly adsorbed CO2. Thus, a major limitation exists with the use of these conventional PSA cycles for high purity CO2 capture. Furthermore, complex dynamic behavior of PSA processes together with the numerical difficulties of the model governed by partial differential and algebraic equations (PDAEs) makes the evaluation and assessment of different operating steps and cycle configurations difficult and time-consuming. Therefore, a systematic methodology is essential to design and optimize PSA cycles to recover both H2 and CO2 at a high purity. Recent advances in large-scale optimization strategies for process synthesis have enabled us to address this issue with the help of a systematic optimization-based formulation. In particular, we present a superstructure-based approach to simultaneously determine optimal cycle configurations and design parameters for PSA units. The superstructure is capable to predict a rich set of different PSA operating steps, which are accomplished by manipulating the bed connections with the help of time dependent control variables. An optimal sequence of operating steps is achieved through the formulation of an optimal control problem with the PDAEs of the PSA system. Numerical results for case-studies related to precombustion CO2 capture from a shifted syngas feed mixture having hydrogen and carbon dioxide are presented. In particular, optimal PSA cycles are synthesized which maximize CO2 recovery or minimize overall power consumption. The results show the potential of the superstructure to predict PSA cycles with purities as high as 99% for H2 and 96% for CO2. Moreover, these cycles can recover more than 92% of CO2 with a power consumption as low as 46.8 kW h/tonne CO2 captured. The approach presented is therefore quite useful for evaluating the suitability of different operating strategies for PSA processes. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900873j