Ghani, MU
1995
An Improved Model for Fixed-Bed Coal Combustion and Gasification: Sensitivity Analysis and Applications
Ghani, M.U.; Radulovic, P.T. and Smoot, L.D.
Fuel, 74:1213-1226, 1995. Funded by ACERC and US Department of Energy/Morgantown Energy Technology Center.
Detailed sensitivity analysis and applications of an improved, comprehensive, one-dimensional model for combustion and gasification of coal in fixed beds, FBED-1, are presented. The effects of the devolatilization, oxidation and gasification submodels on the model predictions are discussed. The product gas compositions predicted by various options for gas-phase chemistry are shown. The effects of five model parameters and on operational variable on the predictions of the model are also presented. The sensitivity analysis presented is quantitative since the boundary conditions for both the feed coal and the feed gas streams are satisfied exactly. The utility of the model as a design and analysis tool is demonstrated by simulating two gasifiers: and METC medium-pressure gasifier, and a PyGas high -pressure staged gasifier. Submodels and areas that need further improvements are identified; among these are submodels for large-particle devolatilization, oxidation and gasification and a robust solution method suitable for stiff, highly non-linear problems. Additional features that should be implemented to develop a model for general industrial applications are also identified. These include provisions for additions and withdrawals of gases at multiple locations and options for different flow configurations.
1994
An Improved Model for Fixed-Bed Coal Combustion and Gasification
Radulovic, P.T.; Ghani, M.U. and Smoot, L.D.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
An improved one-dimensional model for countercurrent oxidation and gasification of coal in fixed beds has been developed. The model incorporates an advanced devolatilization submodel that can predict the evolution rates and the yields of individual gas species and tar. A split, back-and-forth, shooting methods is implemented to exactly satisfy the boundary conditions for both the feed coal and the feed gas streams. An option to switch between equilibrium and non-equilibrium gas phase composition has been added. The model predictions are compared with the experimental data for two coals; a Jetson bituminous coal and a Rosebud subbituminous coal. An illustrative simulation for an atmospheric, air-blown, dry ash, Wellman-Galusha gasifier, fired with the Jetson bituminous coal, is presented. Areas that need additional improvements are identified.
1993
Modeling of Coal Conversion Processes in Fixed Beds
Ghani, M.U.; Radulovic, P.T. and Smoot, L.D.
American Chemical Society, Division of Fuel Chemistry, 38: 1358-1369, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
An advanced, one-dimensional fixed-bed coal gasification and combustion model is presented. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on functional groups and depolymerization, vaporization and cross-linking, oxidation and gasification of char, and partial equilibrium in the gas phase. The model is described by 191 highly non-linear, coupled, first order differential equations. Due to the countercurrent nature of the gas and solids flow the system of equations constitutes a split-boundary value problem that is solved by converting it to an initial value problem. This paper presents a split back-and-forth shooting technique that exactly satisfies conditions at both the upper and the lower boundary and provides significant improvements in the predictions. Comparisons of the predicted and experimental results for an atmospheric, air-blown Wellman-Galusha gasifier fired with Jetson bituminous coal are presented.
User's Manual for FBED-1: Fixed Bed Coal Combustion and Gasification Model with a Generalized Coal Devolatilization Submodel (FG-DVC)
Ghani, M.U.; Hobbs, M.L.; Radulovic, P.T.; Smoot, L.D.; Hamblen, D.G. and Zho, Y.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. III, 1993. Funded by US Department of Energy and Morgantown Energy Technology Center.
A generalized, one-dimensional, heterogeneous, steady state, fixed-bed model for gasification and combustion of coal is presented. The model, referred to as FBED-1, is a design and analysis tool that can be used to simulate a variety of fixed or moving bed gasification, combustion, and devolatilization processes. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, depolymerization, vaporization and crosslinking, oxidation and gasification of char, and partial equilibrium in the gas phase. The conservation equations and boundary conditions are formulated for gas and solid overall continuity, gas and solid energy equations, and gas and solid species or elemental continuity equations. Plug flow is assumed in both the solid and the gas phase with variable axial velocities. Gas phase pressure drop is calculated with the Ergun equation for packed beds. Large coal particle devolatilization is allowed to occur simultaneously with char oxidation and gasification. A generalized, coal devolatilization submodel, FG-DFC, is an important part of the model. Shell progressive or ash segregation, shrinking core char submodel describes oxidation and gasification. Turbulence is not treated formally in the slowly moving bed with low gas velocity, but is included implicitly through model correlations such as the effective heat transfer coefficient. A split, back-and-forth iteration and a Livermore solver for ordinary differential equations, LSODE, are used to solve a highly non-linear, stiff system of differential governing equations. Model formulation and solution method are presented, along with user and implementation guides and a sample problem.
Ghani, MU
1995
An Improved Model for Fixed-Bed Coal Combustion and Gasification: Sensitivity Analysis and Applications
Ghani, M.U.; Radulovic, P.T. and Smoot, L.D.
Fuel, 74:1213-1226, 1995. Funded by ACERC and US Department of Energy/Morgantown Energy Technology Center.
Detailed sensitivity analysis and applications of an improved, comprehensive, one-dimensional model for combustion and gasification of coal in fixed beds, FBED-1, are presented. The effects of the devolatilization, oxidation and gasification submodels on the model predictions are discussed. The product gas compositions predicted by various options for gas-phase chemistry are shown. The effects of five model parameters and on operational variable on the predictions of the model are also presented. The sensitivity analysis presented is quantitative since the boundary conditions for both the feed coal and the feed gas streams are satisfied exactly. The utility of the model as a design and analysis tool is demonstrated by simulating two gasifiers: and METC medium-pressure gasifier, and a PyGas high -pressure staged gasifier. Submodels and areas that need further improvements are identified; among these are submodels for large-particle devolatilization, oxidation and gasification and a robust solution method suitable for stiff, highly non-linear problems. Additional features that should be implemented to develop a model for general industrial applications are also identified. These include provisions for additions and withdrawals of gases at multiple locations and options for different flow configurations.
1994
An Improved Model for Fixed-Bed Coal Combustion and Gasification
Radulovic, P.T.; Ghani, M.U. and Smoot, L.D.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
An improved one-dimensional model for countercurrent oxidation and gasification of coal in fixed beds has been developed. The model incorporates an advanced devolatilization submodel that can predict the evolution rates and the yields of individual gas species and tar. A split, back-and-forth, shooting methods is implemented to exactly satisfy the boundary conditions for both the feed coal and the feed gas streams. An option to switch between equilibrium and non-equilibrium gas phase composition has been added. The model predictions are compared with the experimental data for two coals; a Jetson bituminous coal and a Rosebud subbituminous coal. An illustrative simulation for an atmospheric, air-blown, dry ash, Wellman-Galusha gasifier, fired with the Jetson bituminous coal, is presented. Areas that need additional improvements are identified.
1993
Modeling of Coal Conversion Processes in Fixed Beds
Ghani, M.U.; Radulovic, P.T. and Smoot, L.D.
American Chemical Society, Division of Fuel Chemistry, 38: 1358-1369, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
An advanced, one-dimensional fixed-bed coal gasification and combustion model is presented. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on functional groups and depolymerization, vaporization and cross-linking, oxidation and gasification of char, and partial equilibrium in the gas phase. The model is described by 191 highly non-linear, coupled, first order differential equations. Due to the countercurrent nature of the gas and solids flow the system of equations constitutes a split-boundary value problem that is solved by converting it to an initial value problem. This paper presents a split back-and-forth shooting technique that exactly satisfies conditions at both the upper and the lower boundary and provides significant improvements in the predictions. Comparisons of the predicted and experimental results for an atmospheric, air-blown Wellman-Galusha gasifier fired with Jetson bituminous coal are presented.
User's Manual for FBED-1: Fixed Bed Coal Combustion and Gasification Model with a Generalized Coal Devolatilization Submodel (FG-DVC)
Ghani, M.U.; Hobbs, M.L.; Radulovic, P.T.; Smoot, L.D.; Hamblen, D.G. and Zho, Y.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. III, 1993. Funded by US Department of Energy and Morgantown Energy Technology Center.
A generalized, one-dimensional, heterogeneous, steady state, fixed-bed model for gasification and combustion of coal is presented. The model, referred to as FBED-1, is a design and analysis tool that can be used to simulate a variety of fixed or moving bed gasification, combustion, and devolatilization processes. The model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, depolymerization, vaporization and crosslinking, oxidation and gasification of char, and partial equilibrium in the gas phase. The conservation equations and boundary conditions are formulated for gas and solid overall continuity, gas and solid energy equations, and gas and solid species or elemental continuity equations. Plug flow is assumed in both the solid and the gas phase with variable axial velocities. Gas phase pressure drop is calculated with the Ergun equation for packed beds. Large coal particle devolatilization is allowed to occur simultaneously with char oxidation and gasification. A generalized, coal devolatilization submodel, FG-DFC, is an important part of the model. Shell progressive or ash segregation, shrinking core char submodel describes oxidation and gasification. Turbulence is not treated formally in the slowly moving bed with low gas velocity, but is included implicitly through model correlations such as the effective heat transfer coefficient. A split, back-and-forth iteration and a Livermore solver for ordinary differential equations, LSODE, are used to solve a highly non-linear, stiff system of differential governing equations. Model formulation and solution method are presented, along with user and implementation guides and a sample problem.