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Mathematical modeling of a single - stage, downward - firing, entrained - flow gasifier / Job S. Kasule in Industrial & engineering chemistry research, Vol. 51 N° 18 (Mai 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 18 (Mai 2012) . - pp. 6429-6440 Titre : Mathematical modeling of a single - stage, downward - firing, entrained - flow gasifier Type de document : texte imprimé Auteurs : Job S. Kasule, Auteur ; Richard Turton, Auteur ; Debangsu Bhattacharyya, Auteur Année de publication : 2012 Article en page(s) : pp. 6429-6440 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Modeling  Gasifier Résumé : Gasifiers are the centerpieces of coal-fired integrated gasification combined cycle (IGCC) plants. Mathematical models of gasifiers have been developed in recent literature to describe the physical and chemical processes taking place inside the reactor vessels. These models range from simple one-dimensional (1D) steady-state equilibrium models to higher-order, sophisticated, dynamic 2D and 3D computational fluid dynamics (CFD) models that describe coupled gas―solid hydrodynamics, heat and mass transfer, and reaction kinetics over the complex gasifier geometry. In the current work, a 1D steady-state model of a single-stage, downward-firing, oxygen-blown, slurry-fed, entrained-flow gasifier has been developed for use in the context of IGCC process simulation. In this mathematical model, mass, momentum, and energy balance equations for solid and gas phases are considered. The model includes a number of heterogeneous and homogeneous chemical reactions along with devolatilization and drying of the slurry feed. The solid-gas heterogeneous reaction rates are calculated using the unreacted shrinking-core model A detailed model of the radiative heat transfer has been developed considering interactions between the solids and all internal gasifier surfaces (side wall, top, and bottom surfaces), as well as interactions between the surfaces themselves. No a priori wall temperature profile is assumed in this model. The heat loss from the gasifier wall to the environment is also considered in the energy balance equations. In slurry-fed gasifiers, recirculation near the inlet of the gasifier is promoted by rapid mixing of the slurry feed with a portion of the hot reaction products. This violent mixing results in a significant rise in temperature that helps in evaporating the water and devolatilizing the coal. The recirculation is achieved by appropriately designing the feed burner and feeding the oxygen through a swirling annular injector. In the current gasifier model, a heuristic recirculation model has been developed and the conservation equations have been appropriately modified. The equations describing the gasifier are formulated as a set of ordinary differential equations (ODEs) in Aspen Custom Modeler (ACM). The ODEs are discretized using finite differences, and the resulting highly nonlinear system of algebraic equations is solved using a Newton-type method. The gasifier model is then validated using pilot plant and industrial data. This paper presents a number of parametric studies that have been performed using the 1D steady-state gasifier model to provide insight into the gasifier performance as the inlet and operating conditions change. Results are presented as profiles for species concentration and gas, solid, and wall temperatures. The effect of coal feed types on composition are also presented. In addition, a radiant syngas cooler (RSC) model has been developed in Aspen Plus and coupled with the gasifier model, thereby enabling the RSC exit stream composition to be compared to available industrial data. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202121h [article] Mathematical modeling of a single - stage, downward - firing, entrained - flow gasifier [texte imprimé] / Job S. Kasule, Auteur ; Richard Turton, Auteur ; Debangsu Bhattacharyya, Auteur . - 2012 . - pp. 6429-6440. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 18 (Mai 2012) . - pp. 6429-6440 Mots-clés : Modeling  Gasifier Résumé : Gasifiers are the centerpieces of coal-fired integrated gasification combined cycle (IGCC) plants. Mathematical models of gasifiers have been developed in recent literature to describe the physical and chemical processes taking place inside the reactor vessels. These models range from simple one-dimensional (1D) steady-state equilibrium models to higher-order, sophisticated, dynamic 2D and 3D computational fluid dynamics (CFD) models that describe coupled gas―solid hydrodynamics, heat and mass transfer, and reaction kinetics over the complex gasifier geometry. In the current work, a 1D steady-state model of a single-stage, downward-firing, oxygen-blown, slurry-fed, entrained-flow gasifier has been developed for use in the context of IGCC process simulation. In this mathematical model, mass, momentum, and energy balance equations for solid and gas phases are considered. The model includes a number of heterogeneous and homogeneous chemical reactions along with devolatilization and drying of the slurry feed. The solid-gas heterogeneous reaction rates are calculated using the unreacted shrinking-core model A detailed model of the radiative heat transfer has been developed considering interactions between the solids and all internal gasifier surfaces (side wall, top, and bottom surfaces), as well as interactions between the surfaces themselves. No a priori wall temperature profile is assumed in this model. The heat loss from the gasifier wall to the environment is also considered in the energy balance equations. In slurry-fed gasifiers, recirculation near the inlet of the gasifier is promoted by rapid mixing of the slurry feed with a portion of the hot reaction products. This violent mixing results in a significant rise in temperature that helps in evaporating the water and devolatilizing the coal. The recirculation is achieved by appropriately designing the feed burner and feeding the oxygen through a swirling annular injector. In the current gasifier model, a heuristic recirculation model has been developed and the conservation equations have been appropriately modified. The equations describing the gasifier are formulated as a set of ordinary differential equations (ODEs) in Aspen Custom Modeler (ACM). The ODEs are discretized using finite differences, and the resulting highly nonlinear system of algebraic equations is solved using a Newton-type method. The gasifier model is then validated using pilot plant and industrial data. This paper presents a number of parametric studies that have been performed using the 1D steady-state gasifier model to provide insight into the gasifier performance as the inlet and operating conditions change. Results are presented as profiles for species concentration and gas, solid, and wall temperatures. The effect of coal feed types on composition are also presented. In addition, a radiant syngas cooler (RSC) model has been developed in Aspen Plus and coupled with the gasifier model, thereby enabling the RSC exit stream composition to be compared to available industrial data. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202121h

Modeling studies of a cylindrical polymer electrolyte membrane fuel cell cathode / Srinivasarao Modekurti in Industrial & engineering chemistry research, Vol. 51 N° 13 (Avril 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 13 (Avril 2012) . - pp. 5003–5010 Titre : Modeling studies of a cylindrical polymer electrolyte membrane fuel cell cathode Type de document : texte imprimé Auteurs : Srinivasarao Modekurti, Auteur ; Brian Bullecks, Auteur ; Debangsu Bhattacharyya, Auteur Année de publication : 2012 Article en page(s) : pp. 5003–5010 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Polymer  electrolyte  Fuel  cells Résumé : Traditional polymer electrolyte membrane fuel cells (PEMFCs) are planar. High cost and low gravimetric and volumetric power densities are two major issues with the planar design. To improve the gravimetric and volumetric power densities of the PEMFCs and to reduce the cost, a novel cylindrical PEMFC design has been developed. The performance of the air-breathing cylindrical PEMFC is found to be superior to a state-of-the-art planar cell in the high current density region. To understand the effect of various design parameters and operating conditions on the performance of the cylindrical PEMFC, two-dimensional, two-phase, steady-state models of the cylindrical cell for both air-breathing and pressurized conditions have been developed in this work. The developed model of the air-breathing cylindrical PEMFC is validated with in-house experimental data. Experiments were conducted with hydrogen on the anode side and air on the cathode side. The cathode catalyst layer is modeled using spherical agglomerate characterization. With the developed model, the effects of various operating and design parameters on the performance of the cell are studied. These studies show that the performance of the cylindrical cell can be further improved by optimizing these parameters. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie2028359 [article] Modeling studies of a cylindrical polymer electrolyte membrane fuel cell cathode [texte imprimé] / Srinivasarao Modekurti, Auteur ; Brian Bullecks, Auteur ; Debangsu Bhattacharyya, Auteur . - 2012 . - pp. 5003–5010. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 13 (Avril 2012) . - pp. 5003–5010 Mots-clés : Polymer  electrolyte  Fuel  cells Résumé : Traditional polymer electrolyte membrane fuel cells (PEMFCs) are planar. High cost and low gravimetric and volumetric power densities are two major issues with the planar design. To improve the gravimetric and volumetric power densities of the PEMFCs and to reduce the cost, a novel cylindrical PEMFC design has been developed. The performance of the air-breathing cylindrical PEMFC is found to be superior to a state-of-the-art planar cell in the high current density region. To understand the effect of various design parameters and operating conditions on the performance of the cylindrical PEMFC, two-dimensional, two-phase, steady-state models of the cylindrical cell for both air-breathing and pressurized conditions have been developed in this work. The developed model of the air-breathing cylindrical PEMFC is validated with in-house experimental data. Experiments were conducted with hydrogen on the anode side and air on the cathode side. The cathode catalyst layer is modeled using spherical agglomerate characterization. With the developed model, the effects of various operating and design parameters on the performance of the cell are studied. These studies show that the performance of the cylindrical cell can be further improved by optimizing these parameters. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie2028359

A review of solid oxide fuel cell (SOFC) dynamic models / Debangsu Bhattacharyya in Industrial & engineering chemistry research, Vol. 48 N° 13 (Juillet 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 13 (Juillet 2009) . - pp. 6068–6086 Titre : A review of solid oxide fuel cell (SOFC) dynamic models Type de document : texte imprimé Auteurs : Debangsu Bhattacharyya, Auteur ; Raghunathan Rengaswamy, Auteur Année de publication : 2009 Article en page(s) : pp. 6068–6086 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : State-of-the-art  dynamic  models  Solid  oxide  fuel  cells  Dynamic  modeling Résumé : In this paper, state-of-the-art dynamic models for solid oxide fuel cells (SOFCs) in the open literature are reviewed. The review also includes the transient modeling of SOFC systems with reformers. In the transients of a SOFC, three characteristic time constants are observed. One of the challenges in transient modeling is to capture these characteristic times. The first characteristic time is on the order of milliseconds and is mostly neglected, because it is too small, from the viewpoint of practical applications. The second time constant is on the order of seconds and arises mainly because of the mass-transport dynamics. The third characteristic time is on the order of minutes or hours and is dependent on the energy transport characteristics of the system. These characteristic times are extremely system-specific and, therefore, must be identified on a case-to-case basis. In this paper, the existing literature on dynamic studies are reviewed, focusing mainly on the fidelity of the model that is required to capture these time constants. The dynamic modeling of SOFC is still not as rich as the steady-state modeling. Therefore, steady-state models are also reviewed, whenever required. The utility of the dynamic models in design, control, and operation is discussed. A dynamic model from the literature is chosen for this purpose. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801664j [article] A review of solid oxide fuel cell (SOFC) dynamic models [texte imprimé] / Debangsu Bhattacharyya, Auteur ; Raghunathan Rengaswamy, Auteur . - 2009 . - pp. 6068–6086. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 13 (Juillet 2009) . - pp. 6068–6086 Mots-clés : State-of-the-art  dynamic  models  Solid  oxide  fuel  cells  Dynamic  modeling Résumé : In this paper, state-of-the-art dynamic models for solid oxide fuel cells (SOFCs) in the open literature are reviewed. The review also includes the transient modeling of SOFC systems with reformers. In the transients of a SOFC, three characteristic time constants are observed. One of the challenges in transient modeling is to capture these characteristic times. The first characteristic time is on the order of milliseconds and is mostly neglected, because it is too small, from the viewpoint of practical applications. The second time constant is on the order of seconds and arises mainly because of the mass-transport dynamics. The third characteristic time is on the order of minutes or hours and is dependent on the energy transport characteristics of the system. These characteristic times are extremely system-specific and, therefore, must be identified on a case-to-case basis. In this paper, the existing literature on dynamic studies are reviewed, focusing mainly on the fidelity of the model that is required to capture these time constants. The dynamic modeling of SOFC is still not as rich as the steady-state modeling. Therefore, steady-state models are also reviewed, whenever required. The utility of the dynamic models in design, control, and operation is discussed. A dynamic model from the literature is chosen for this purpose. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801664j

System identification and nonlinear model predictive control of a solid oxide fuel cell / Debangsu Bhattacharyya in Industrial & engineering chemistry research, Vol. 49 N° 10 (Mai 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 10 (Mai 2010) . - pp. 4800–4808 Titre : System identification and nonlinear model predictive control of a solid oxide fuel cell Type de document : texte imprimé Auteurs : Debangsu Bhattacharyya, Auteur ; Raghunathan Rengaswamy, Auteur Année de publication : 2010 Article en page(s) : pp. 4800–4808 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Nonlinear  system  Oxide  fuel  cell Résumé : Solid oxide fuel cells (SOFCs) are high temperature fuel cells with a strong potential for stationary power house applications. However, considerable challenges need to be overcome to connect these cells to the power grid. The fluctuating grid demand has to be met without sacrificing the cell efficiency and causing structural/material damage to the system. This requirement coupled with fast and highly nonlinear transients of the transport variables results in a challenging control problem. This paper is on synthesizing a controller that can address some of these challenges. For using in the model predictive controller (MPC), input−output models are identified from the data generated by a detailed dynamic model. A traditional SISO control and a novel MIMO control are considered here. In the SISO control problem, power is the controlled variable (CV) and H2 flow is the manipulated variable (MV). In the MIMO control problem, power and the utilization factor (UF) of the fuel are the CVs while voltage and the flow of H2 are the MVs. The identification study shows that the nonlinear NAARX models with properly chosen cross terms can improve the model performance significantly in a MIMO problem. The results from the control study indicate that a well-tuned proportional−integral−derivative (PID) controller is sufficient for the single input single output (SISO) power control of a tubular SOFC. It also shows that the mutiple input multiple output (MIMO) control of power and the UF is highly interactive and necessitates a nonlinear model predictive controller (NMPC). Without using any additional hardware such as an ultracapacitor or battery pack, the designed NMPC could satisfy a step change in load with acceptable overshoot in power and the UF. A well-tuned PID controller is found to perform poorly for the MIMO problem. On the basis of these findings, future work will focus on the development of nonlinear predictive control approaches for stack-level control of tubular solid oxide fuel cells. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9020254 [article] System identification and nonlinear model predictive control of a solid oxide fuel cell [texte imprimé] / Debangsu Bhattacharyya, Auteur ; Raghunathan Rengaswamy, Auteur . - 2010 . - pp. 4800–4808. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 10 (Mai 2010) . - pp. 4800–4808 Mots-clés : Nonlinear  system  Oxide  fuel  cell Résumé : Solid oxide fuel cells (SOFCs) are high temperature fuel cells with a strong potential for stationary power house applications. However, considerable challenges need to be overcome to connect these cells to the power grid. The fluctuating grid demand has to be met without sacrificing the cell efficiency and causing structural/material damage to the system. This requirement coupled with fast and highly nonlinear transients of the transport variables results in a challenging control problem. This paper is on synthesizing a controller that can address some of these challenges. For using in the model predictive controller (MPC), input−output models are identified from the data generated by a detailed dynamic model. A traditional SISO control and a novel MIMO control are considered here. In the SISO control problem, power is the controlled variable (CV) and H2 flow is the manipulated variable (MV). In the MIMO control problem, power and the utilization factor (UF) of the fuel are the CVs while voltage and the flow of H2 are the MVs. The identification study shows that the nonlinear NAARX models with properly chosen cross terms can improve the model performance significantly in a MIMO problem. The results from the control study indicate that a well-tuned proportional−integral−derivative (PID) controller is sufficient for the single input single output (SISO) power control of a tubular SOFC. It also shows that the mutiple input multiple output (MIMO) control of power and the UF is highly interactive and necessitates a nonlinear model predictive controller (NMPC). Without using any additional hardware such as an ultracapacitor or battery pack, the designed NMPC could satisfy a step change in load with acceptable overshoot in power and the UF. A well-tuned PID controller is found to perform poorly for the MIMO problem. On the basis of these findings, future work will focus on the development of nonlinear predictive control approaches for stack-level control of tubular solid oxide fuel cells. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9020254