Brewster, BS
1999
PDF Modeling of Lean Premixed Combustion Using In Situ Tabulated Chemistry
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, 119:233-252 (1999).
The velocity-composition probability density function (pdf) model coupled with a k-?-based mean flow computational fluid dynamics (CFD) model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a bluff-body, lean, premixed, methane-air combustor. Measured data [1,2] including velocity, temperature, and chemical species concentrations were used to evaluate the model. The chemistry calculations were performed with an in situ look-up tabulation method [3]. A reduced, 5-step chemical mechanism [4] for describing fuel oxidation, CO, and NO chemistry was used in the model. NO formation from thermal, N2O-intermediate, and prompt pathways was included in the 5-step mechanism. An axisymmetric, unstructured grid was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle equations. Predicted velocity and composition mean statistics were compared to measurements in the bluff-body combustor for a lean equivalence ratio of 0.59. The predictions of major species matched measured and calculated equilibrium values in the recirculation zone. Comparisons of mean CO throughout the combustor were always within an order of magnitude and showed marked improvements over past predictions. Maximum discrepancies between measured and predicted NO concentrations were between 5 and 7 ppm (~50%). The accessed composition space in this turbulent combustion simulation represented the values of species mole fraction and enthalpy for each fluid particle at each time step and was found to lie in a relatively small, uniquely shaped region that was dictated by the mixing, reaction, and heat transfer in the combustor. This accessed composition region was obtained in situ and required about 35 megabytes of storage once a steady state was reached. This memory requirement was more than three orders of magnitude less than would be needed in a standard, a priori table. The in situ tabulation approach allowed for technically correct and efficient chemical kinetic calculations by using the 5-step mechanism in this pdf-method-based, multidimensional combustor model.
1998
Stochastic Modeling of CO and NO in Premixed Methane Combustion
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, 113:135-146 (1998).
The ability to use reduced CH4-air chemical mechanisms to predict CO and NO emissions in premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with reduced 4-, 5-, and 9-step mechanisms and a detailed 276-step mechanism. NO emissions from thermal, N2O-intermediate, and prompt pathways were included in the 5-, 9-, and 276-step mechanisms. Molecular mixing was described with a deterministic, Interaction-by Exchange-with-the-Mean (IEM) submodel. Random selection and replacement (without repetition) of fluid particles were used to simulate through-flow. The evolution of mean and root mean square (rms) temperature, CO, and NO in the PaSR was accurately described with the 9-step mechanism over a wide range in mixing frequency and equivalence ratio. Also, the 9-step mechanism provided accurate instantaneous reaction rates and concentrations for a broad region of the accessed composition space in the PaSR. The 5-step mechanism performed less reliably than the 9-step mechanism at phi = 1.0 but performed similarly to the 9-step mechanism at phi = 0.65. The 4-step mechanism underpredicted mean CO values and overpredicted instantaneous temperature reaction rates, most likely due to its inferior parent mechanism, partial equilibrium assumption for OH, and unallowed dissociation of neglected radical species. The detailed and reduced mechanism predictions of the accessed composition space in the PaSR covered only a small fraction of the allowable composition space, thus facilitating the use of an efficient in situ chemical look-up table for multidimensional, pdf-method calculations.
1997
Stochastic Modeling of CO and NO in Premixed Methane Combustion
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, (in press), 1997. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NO emission in premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with reduced 4-, 5-, and 9-step mechanisms and a detailed 276-step mechanism. NO emissions from thermal N2O-intermediate and prompt pathways were included in the 5-, 9- and 276-step mechanisms. Molecular mixing was described with a deterministic, Interaction-by-Exchange-with-the-Mean (IEM) submodel. Random selection and replacement (without repetition) of fluid particles was used to simulate through-flow. The evolution of mean and rms temperature, CO, and NO in the PaSR was accurately described with the 9-step mechanisms over a wide range in mixing frequency and equivalence ratio. Also, the 9-step mechanism provided accurate instantaneous reaction rates and concentrations for a broad region of the accessed composition space in the PaSR. The 5-step mechanism performed less reliably than the 9-step mechanism at phi = 1.0 but performed similarly to the 9-step mechanism at phi = 0.65. The 4-step mechanism underpredicted mean CO values and overpredicted instantaneous temperature reaction rates, most likely due to its inferior parent mechanism, partial equilibrium assumption for OH, and unallowed dissociation of neglected radical species. The detailed reduced mechanism predictions of the accessed composition space in the PaSR covered only a small fraction of the allowable composition space, thus facilitating the use of an efficient, in situ chemical look-up table in multi-dimensional, pdf-method calculations.
Comprehensive Model for Lean Premixed Combustion in Industrial Gas Turbines - Part I. Validation
Cannon, S.M.; Brewster, B.S.; Smoot, L.D.; Murray, R. and Hedman, P.O.
Presented at the Spring Meeting of the Western States Section/The Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy.
The velocity composition pdf model coupled with a mean flow CFD model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a swirling, lean premixed, methane-air combustor for which laser-based measurements of mean velocity and temperature were made. A flame was stabilized in this axi-symmetric, lab-scale, gas-turbine combustor (LSGTC. A reduced, 5-step chemical mechanism, for describing fuel oxidation and NO chemistry, was used in this LSGTC model. NO emissions from thermal, N2)-intermediate, and prompt pathways were described with this 5-step mechanism. The chemistry calculations were performed efficiently with and in-situ look-up table. An axi-symmetric, unstructured grid consisting of 2283 vertices and 4302 triangular elements was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle (~310,000 fluid particles) equations. Predicted velocity and composition statistics were compared to measurements in the LSGTC for lean equivalence ratios of 0.8 and 0.65. The comparisons of predicted mean velocity and temperature were reasonable good throughout the combustor. The location and magnitude of peak axial velocity was well represented by the model at near inlet regions, through the negative mean axial velocity in the internal recirculation zone was over-predicted. The predicted maximum mean temperature and the penetration zone of the cold unburned fluid were in reasonable agreement with the experimental data. Correct trends in CO and NO with equivalence ration were predicted with the model. The in situ tabulation method was used to represent the chemical kinetics in this axi-symmetric combustor without requiring significant CPU time and memory. The model is currently being applied to simulate 3-dimensional, gas-turbine combustor geometries and is described in a companion paper.
Comprehensive Model for Lean Premixed Combustion in Industrial Gas Turbines - Part II. Application
Meng, F.L.; Brewster, B.S. and Smoot, L.D.
Presented at the Spring Meeting of the Western States Section/The Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy.
A new comprehensive COmbustion Simulation MOdel for Gas Turbines (COSMO/GT) has been developed for simulating modern gas turbine combustors. The model includes the capability of simulating lean premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. In our earlier paper we extended the velocity-composition PDF approach to an unstructured grid platform for modeling two-dimensional, axisymmetric, lean premixed turbulent combustion in a lab-scale gas turbine combustor. In this paper, the extension of this PDF approach to a three-dimensional, unstructured grid is reported. The turbulence/chemistry interaction is modeled using the velocity-composition, Monte-Carlo PDF approach coupled with a five-step kinetic mechanism of methane and air for calculating CO and NO emissions. In order to increase the calculation speed of the PDF algorithm, in situ tabulation for chemical reaction and a zonal search method for locating particle positions are used. Validation of this model for and axisymmetric, lab-scale gas turbine combustor is described in a companion paper. Application of this model has been initiated by modeling lean, premixed combustion of natural gas and air in three-dimensional gas turbine combustors.
1996
Model Comparisons with Drop Tube Combustion Data for Various Devolatilization Submodels
Brewster, B.S.; Smoot, L.D. and Barthelson, S.H.
Energy & Fuels, 9:870-878, 1996. Funded by ACERC.
Predictions of a two-dimensional, axisymmetric combustion model, using various devolatilization submodel options, are compared with new experimental data from a near-laminar, drop-tube furnace. Included in the devolatilization submodels that were teste are the commonly used empirical one-and two-step models and a chemical, coal network model with parameters based on coal structure. The goals of this work were to evaluate the latter approach as compared with the simple, empirical approach usually used in such calculations and to assess the role of turbulence in a near-laminar reacting flow. Comparisons were made for carbon conversion, radially averaged oxygen and near-effluent NOX concentrations, for a range of coal types and equivalence ratios. The predictions quantify an ignition delay that is consistent with the measurements. Computations with the fundamental, chemical devolatilization submodel gave superior predictions of mass loss when the coal type was within the interpolation range of the submodel parameter database. Accuracy declined significantly when the coal type was outside the interpolation range. Inclusion of the effects of turbulence was required to account for the observations. Near effluent NO predictions with the chemical submodel agreed with measured NOX values to within an average of about 20 percent.
Modeling of Industrial Gas Turbine Combustors
Meng, F.L.; Farmer, J.R.; Brewster, B.S. and Smoot, L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section / The Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC.
A new model has been developed for simulating modern gas turbine combustors. The new model includes the capability of simulating lean, premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. The set of incompressible, steady state, Navier-Stokes equations is solved using a co-located, equal-order, control volume finite element method. The convection term is treated using the mass-weighted, skew upwind scheme, and the diffusion, pressure gradient, and source terms are interpolated linearly in each element. Turbulence is modeled using the kappa-epsilon model. Convective and radiative heat losses are modeled using a wall function method and a discrete ordinates method, respectively. The interaction between turbulence and chemistry is modeled using the velocity-composition Monte-Carlo PDF approach, coupled with a multiple-step reaction mechanism for methane and air. Validation of the code has been initiated by modeling lean, premixed combustion (Phi = 0.8) of natural gas and air in a laboratory-scale, gas turbine combustor with a simple, two-step kinetic mechanism for CH4-O2. Comparison with detailed measurements is forthcoming. Application to industrial gas turbine combustor components is also underway.
Prediction of CO and NOx in Lean Premixed Turbulent Combustion
Cannon, S.M.; Brewster, B.S. and Smoot L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section/The Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NOx emissions in lean premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with mathematically reduced 4-, 5- and 9-step mechanism and a detailed 276-step mechanism. NOx emission form thermal, N2O-intermediate, and prompt pathways were described with the 5-, and 9-step reduced mechanisms provided accurate instantaneous reaction rate calculations for a broad region of the accessed composition space in the PaSR. The 4-step mechanism and the partial equilibrium assumption for OH. Practicality of using the 5- and 9-step mechanisms in industrial, 3-dimensional calculations may require the use of a novel, in situ look-up table.
1994
Fossil-Fuel Conversion - Measurement and Modeling
Solomon, P.R.; Serio, M.A.; Hamblen, D.G.; Smoot, L.D.; Brewster, B.S. and Radulovic, P.T.
Proceedings of the Coal-Fired Power Systems 94 - Advances in IGCC and PFBC Review Meeting, Morgantown, West Virginia, June 1994. Funded by US Department of Energy/Morgantown Energy Technology Center.
The main objective of this program is to understand the chemical and physical mechanisms in coal conversion processes and incorporate this technology for the purposes of development, evaluation in advanced coal conversion devices. To accomplish this objective, this program will: 1) provide critical data on the physical and chemical processes in fossil fuel gasifiers and combustors; 2) further develop a set of comprehensive codes; and 3) apply these codes to model various types of combustors and gasifiers (fixed-bed transport reactor, and fluidized-bed for coal and gas turbines for natural gas).
To expand the utilization of coal, it is necessary to reduce the technical and economic risks inherent in operating a feedstock which is highly variable and which sometimes exhibits unexpected and unwanted behavior. Reducing the risks can be achieved by establishing the technology to predict a coal's behavior in a process. This program is creating this predictive capability by merging technology developed at Advanced Fuel Research, Inc. (AFR) in predicting coal devolatilization behavior with technology developed at Brigham Young University (BYU) in comprehensive computer codes for modeling of entrained-bed and fixed-bed reactors and technology developed at the U.S. DOE-METC in comprehensive computer codes for fluidized-bed reactors. These advanced technologies will be further developed to provide: 1) a fixed-bed model capable of predicting combustion and gasification of large coal particles, 2) a transport reactor model, 3) a model for lean premixed combustion of natural gas, and 4) an improved fluidized-bed code with an advanced coal devolatilization chemistry submodel.
1993
Development and Application of an Acid Rain Precursor Model for Practical Furnaces
Smoot, L.D.; Boardman, R.D.; Brewster, B.S.; Hill, S.C. and Foli, A.K.
Energy & Fuels, 7 (6):786-795, 1993. Funded by ACERC.
Control of emissions of sulfur (SO2, SO3, H2S) and nitrogen (NO, NO2, N2O, HCN, NH3) pollutants from fossil-fuel-fired furnaces and gasifiers remains a vital worldwide requirement as the utilization of fossil fuels continues to increase. Development and refinement of a predictive model for these acid rain precursors (MARP) has reached the point where this technology can contribute to acid rain control. In this paper, model foundations and recent developments are summarized, including formation of thermal and fuel NOx and sorbent capture of sulfur oxides. The method includes global formation, capture, and destruction processes in turbulent, reacting, particle-laden flows. This submodel has been combined with comprehensive, generalized combustion models (PCGC-2, PCGC-3) that provide the required local properties for the combustion or gasification processes. The submodel has been applied to NOx formation in a full-scale (85 MWe), corner-fired utility boiler, where recent in situ NOx measurements were made, with variations in coal feedstock quality (including fuel N percentage) load-level and percentage excess air. Predictions are also made for in situ sorbent capture of sulfur pollutants in both combustion (fuel-lean, SO2), and gasification (fuel-rich, H2S) laboratory-scale reactors. Limitations of MARP are identified and work to improve the submodel is outlined.
Comprehensive Modeling
Brewster, B.S.; Hill, S.C.; Radulovic, P.T. and Smoot, L.D.
Chapter 8, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter treats comprehensive modeling of combustion and gasification systems. Entrained, fluidized and fixed bed models are considered. Single and multidimensional models are reviewed. Developing comprehensive computer models to help design combustors and gasifiers for clean and efficient utilization of coal and other fossil fuels is a primary objective of ACERC. Such models provide not only a framework for effectively integrating combustion-related technology from a wide array of disciplines, but a vehicle for transferring this technology to industry. In order to be useful, these models must satisfy at least three criteria: First, the input and output must be easily accessible (user-friendly graphics must play a role here). Second, the computer algorithms must be robust and computationally efficient. And third, the models must be thoroughly evaluated to demonstrate applicability to industrial processes and to justify confidence in their predictions. Developing and implementing user-friendly, robust, efficient, applicable, accurate models requires significant, on-going effort that is reviewed herein.
Structure of a Near-Laminar Coal Jet Flame
Brewster, B.S. and Smoot, L.D.
Energy & Fuels, 7 (6):884-890, 1993. Funded by US Department of Energy.
Flame data from a near-laminar coal jet have been compared with model predictions. Inclusion of gas turbulence with laminarization was necessary for adequately predicting the upper-flame and postflame regions and for predicting particle dispersion. Dispersion of gas and particles was insensitive to inlet turbulence intensity. Gas buoyancy induced radially inward flow that opposed particle dispersion. Gas temperature was predicted too high near the coal nozzle, perhaps due to neglecting finite-rate mixing of volatiles with the bulk gas and chemical kinetics effects. Single-particle burning effects were important in the flame zone, as evidenced by the sensitivity of particle temperature to direct enthalpy feedback from volatiles combustion. Particle burnout was insensitive to enthalpy feedback, heterogeneous CO2 formation, and chemistry/turbulence interaction.
User's Manual for 93-PCGC-2:Pulverized Coal Gasification and Combustion Model (2-Dimensional) with Generalized Coal Reactions Submodel FG-DVC
Brewster, B.S.; Boardman, R.D.; Huque, Z.; Berrondo, S.K.; Eaton, A.M.; Smoot, L.D.; Zhao, Y.; Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Charpenay, S.; Best, P.E. and Yu, Z.-Z.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. II, 1993. Funded by US Department of Energy and Morgantown Energy Technology Center.
A two-dimensional, steady-state model for describing a variety of reactive and non-reactive flows, including pulverized coal combustion and gasification, is presented. Recent code revisions and additions are described. The model, referred to as 93-PCGC-2, is applicable to cylindrical, axi-symmetric systems. Turbulence is accounted for in both the fluid mechanics equations and the combustion scheme. Radiation from gases, walls, and particles is taken into account using a discrete ordinates method. The particle phase is modeled in a Lagrangian framework, such that mean paths of particle groups are followed. A new coal-general devolatilization submodel (FG-DVC) with coal swelling and char reactivity submodels has been added. The heterogeneous reaction scheme allows for both diffusion and chemical reaction. Major gas-phase reactions are modeled assuming local instantaneous equilibrium, and thus the reaction rates are limited by the turbulent rate of mixing. A thermal and fuel NOx finite rate chemistry submodel is included which integrates chemical kinetics and the statistics of the turbulence. A sorbent injection submodel with sulfur capture is included. The gas phase is described by elliptic partial differential equations that are solved by an iterative line-by-line technique. Under-relaxation is used to achieve numerical stability. Both combustion and gasification environments are permissible. User information and theory are presented, along with sample problems.
Measurement and Modeling of Advanced Coal Conversion Processes
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. I, 1993. (Also presented at the Coal-fired power systems 93 Conference, Morgantown, WV, June 1993.) Funded by US Department of Energy and Morgantown Energy Technology Center. (This report is available from Advanced Fuel Research, Inc.)
This project included research in the following areas: (1) fundamental high-pressure reaction rate data; (2) large particle oxidation at high pressures; (3) SOx-NOx submodel development; (3) integration of advanced submodels into entrained-flow code, with evaluation and documentation; (4) comprehensive fixed-bed modeling, review, development, evaluation and implementation; (5) generalized fuels feedstock submodel; (6) application of generalized pulverized coal comprehensive code and (7) application of fixed-bed code.
1992
Modeling Sorbent Injection and Sulfur Capture in Pulverized Coal Combustion
Boardman, R.D.; Brewster, B.S.; Huque, Z.; Smoot, L.D. and Silcox, G.D.
Air Toxic Reduction and Combustion Modeling, 15:1-9, 1992. (Also presented at the ASME International Joint Power Generation Conference, Atlanta, GA, October 1992). Funded by Advanced Fuel Research and ACERC.
A computer model has been developed for predicting mixing and reactions of injected sorbent particles in pulverized coal combustors and gasifiers. A shrinking-core, grain model was used for sulfation. The model accounts for the effects of surface area, pore diffusion, diffusion through the product layer, chemical reaction, and reduction of the pore volume due to grain swelling. The submodel was evaluated for a fuel-lean case and for a fuel-rich case. Predictions were compared with limited experimental data (for the fuel-rich case). The results illustrate the model's capability for predicting the effectiveness of sulfur capture. The importance of sorbent particle properties was also investigated parametrically, and model limitations were identified.
Application of Coal-General, 2-D Combustion Model
Brewster, B.S.
Ninth Annual Pittsburgh Coal Conference, Pittsburgh, PA, October 1992. Funded by Advanced Fuel Research.
A 2-D combustion model with advanced submodels for coal reactions and pollutants was used to simulate a cyclone combustor. Predicted gas velocity, coal particle trajectories, burnout, and sulfur capture by injected sorbent are presented. Particle trajectories are predicted to be very sensitive to particle size. The predictions give insight into the effects of reactor L/D ratio, coal; and sorbent particle size distribution, and optimal slag tap location. Needed model improvements include accounting for particle rebounding, sorbent calcinations and sintering, and sorbent particle dynamics. A 3-D model is needed to investigate the effects of particle injection geometry.
Comprehensive Fixed-Bed Modeling, Review, Development, Evaluation, and Implementation
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
21st, 22nd, and 23rd Quarterly Reports for the US Department of Energy, 1992. Funded by US Department of Energy and Morgantown Energy Technology Center.
The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal, a feedstock whose variable and often unexpected behavior presents a significant challenge. This program is merging significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation is being implemented and the technology was expanded to fixed-bed reactors. The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model has been integrated with BYU's comprehensive two-dimensional reactor mode, PCGC-2, which is a widely used reactor simulation for combustion or gasification. The program includes: 1) validation of the submodels by comparison with laboratory data obtained in this program, 2) extensive validation of the modified comprehensive code by comparison of predicted results with data from bench-scale and process scale investigations of gasification, mild gasification and combustion of coal or coal-derived products in heat engines, and 3) development of well documented user friendly software applicable to a "workstation" environment.
1991
Measurements and Modeling of Advanced Coal Conversion Processes: Fixed-Bed Coal Gasification Modeling
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
Contractors Review Meeting, Morgantown, WV, August 1991. Funded by Morgantown Energy Technology Center.
The overall objective of this program is to understand the chemical and physical mechanisms in coal conversion processes and incorporate this knowledge in computer-aided reactor engineering technology for the purposes of development, evaluation, design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. To accomplish this objective, the study will: establish the mechanisms and rates of basic steps in coal conversion processes, incorporate this information into comprehensive computer models for coal conversion processes, evaluate these models, and apply them to gasification, mild gasification and combustion in heat engines.
Measurement and Modeling of Advanced Coal Conversion Processes
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
5th Annual Report for the US Department of Energy, 1991. Funded by Morgantown Energy Technology Center.
The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal a feedstock whose variable and often unexpected behavior presents a significant challenge. This program will merge significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation will be implemented and the technology will be expanded to fixed-bed reactors.
The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model will be integrated with BYU's comprehensive two-dimensional reactor model, PCGC-2, which is currently the most widely used reactor simulation for combustion or gasification. The program includes: i) validation of the submodels by comparison with laboratory data obtained in this program, ii) extensive validation of the modified comprehensive code by comparison of predicted results with data from bench-scale and process scale investigations of gasification, mild gasification and combustion of coal or coal-derived products in heat engines, and iii) development of well documented user friendly software applicable to a "workstation" environment. Success in this program will be a major step in improving the predictive capabilities for coal conversion processes including: demonstrated accuracy and reliability and a generalized "first principles" treatment of coals based on readily obtained composition data. The progress during the fifth year of the program is summarized in the document.
1990
Structure of a Near-Laminar Coal Jet Flame
Brewster, B.S.; Smoot, L.D.; Solomon, P.R. and Markham, J.R.
Tenth Annual Gasification and Gas Stream Cleanup Systems Contractors Review Meeting, Morgantown, WV, 1990. (Also Presented at the Western States Section/The Combustion Institute, San Diego, CA, 1990). Funded by Morgantown Energy Technology Center and Advanced Fuel Research Co.
An advanced 2-D model for pulverized-coal combustion has been modified and applied to a laminar coal flame in a transparent wall reactor. Modifications were made to allow for the up-fired flow configuration, laminarization, and gas buoyancy. A laminarization extension to the k- turbulence model was incorporated. Particle dispersion is sensitive to laminarization and to the value of turbulent particle Schmidt number. Predicted particle velocity and residence time are sensitive to the inclusion of gas buoyancy, which increases the velocity in the center of the reactor and induces a radial, inward flow. Model predictions have been compared with flame measurements to evaluate the comprehensive model that incorporates an advanced devolatilization submodel. Predicted velocities of burning particles agree well with values determined from particle streaks on video recording. Good agreement was also obtained between measured and predicted particle burnout. Discrepancies between measured and predicted particle and gas temperature may be due to neglecting heterogeneous formation of CO2 and the variation of char reactivity with extent of burnout. Discrepancies between predicted bulk gas temperature and measured CO2 gas temperature in the ignition zone can also be explained by the fact that the combustion energy first heats the CO2 that subsequently heats the other gases. Soot decays more slowly than predicted from equilibrium concentrations of condensed carbon.
1989
Measurement and Prediction of Thermal and Fuel NOx
Boardman, R.D.; Smoot, L.D. and Brewster, B.S.
Western States Section, The Combustion Institute, Livermore, California, 1989. Funded by US Department of Energy through subcontract from Advanced Fuel Research Co., and ACERC (National Science Foundation and Associates and Affiliates).
A generalized NOx model is being developed to predict nitric oxide formation in practical combustors. The NOx model incorporates an extended global fuel-NO mechanism and the modified Zeldovich mechanism to predict thermal NO formation. The importance of coupling turbulence with the chemical kinetics for practical combustors is addressed. Thermal NO data for a turbulent gaseous diffusion flame (in a laboratory-scale furnace) are presented. The model is being validated using these previously unpublished data and other pulverized-coal combustion and gasification data from the literature.
1988
Treatment of Coal Devolatilization in Comprehensive Combustion Modeling
Brewster, B.S.; Baxter, L.L. and Smoot, L.D.
Energy & Fuels, 2, (4), 362-370, 1988. 9 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
Comprehensive combustion codes typically use simple empirical models to predict weight loss associated with coal devolatilization. Individual evolved species are not taken into account nor are the individual products of heterogeneous char reaction. The effects of all particle reactions are lumped into a single overall rate of weight loss, and coal off gas composition and heating value are assumed constant. More detailed devolatilization models that consider the evolution of individual species and predict both rate and composition of the volatiles are now available. These models use general kinetic parameters for each coal constituent that are nearly independent of rank. Such models provide a basis for predicting composition and heating value of the volatiles as a function of burnout and reactor conditions for a wide range of coals. This paper presents a generalized theory based on the existing coal gas mixture fraction model, which allows the variation of off gas composition and heating value to be taken into account in comprehensive code predictions. Results are presented for a swirling combustion case. Results illustrating code sensitivity to several thermal parameters affecting devolatilization and to turbulent fluctuations are also presented. This publication also relates directly to Thrust Area 4.
Predicted Effects of Coal Volatiles Composition in Turbulent Flames
Brewster, B.S. and Smoot, L.D.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 22 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
The predicted effects of turbulence on the mean gas properties in coal combustors have been shown previously to be significant (Smith and Fletcher, 1986; Brewster, et al., 1988). These effects have been incorporated in comprehensive models by the statistical, coal-gas mixture fraction method (Smoot and Smith, 1985), which is based on the scalar approach for gas diffusion flames. Previously, only a single progress variable has been used for tracking coal off gas, including all material originating in the coal and transferring to the gas during the reaction process. Simple weight-loss models for devolatilization have been adequate for this approach that assumes constant off gas composition. With recent technological advances, the incorporation of detailed devolatilization models into comprehensive codes has become a practical consideration. However, detailed models that predict varying off gas composition require improved and/or extended methods of accounting for the effects of turbulence/chemistry interactions for successful incorporation.
In a recent paper, Brewster et al. (1988) presented a generalized formulation of the coal-gas mixture fraction method which allows for an arbitrary number of progress variables, thus allowing each element, or group of elements that evolve at similar rates, to be tracked independently. Independence of the progress variables was assumed, although it would not be difficult to include correlation coefficients if they were known. Results were presented for a slightly fuel-lean, swirling combustion case to illustrate the method. Two progress variables were used to separately track coal volatiles and char off gas, and significant decreases in the size of the fuel-rich region and in coal burnout were noted. These differences were attributed to the enriched oxygen content and (apparently) decreased heating value of the early off gas in the case of two progress variables. In this paper, additional results with multiple progress variables tracking coal off gas are reported and discussed. Calculations using an alternative method of calculating char off gas enthalpy agree qualitatively with previous observations of the effects of tracking volatiles and char off gas separately in combustion. Similar calculations in an oxygen-brown, fuel-rich gasification case show relatively little effect. Even less effect is observed when hydrogen from the coal is tracked separately and all of the other elements are lumped together. The effect of tracking volatiles separately decreased when ultimate volatile yield was increased from 40 to 80 percent, and noticeable differences existed with 50 percent heat loss (uniform) from the reactor compared to no differences when the reactor was assumed to be adiabatic. See also 1-88-J09 which relates to this Thrust Area.
Numerical Model of a Moving-Bed Coal Reactor
Yi, S.C.; Smoot, L.D. and Brewster, B.S.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
A literature review of existing models for moving-bed coal gasifiers and combustors was conducted, and three available 2-D codes were installed and tested. Predictions and sensitivity analyses of the 2-D code developed by Washington University (Bhattacharya et al., 1986) were performed. Based on the review, the proposed features of an advanced model incorporating detailed coal chemistry submodels were identified. One major difference between the proposed model and the existing models is that the proposed model will have separate gas and solids temperatures. As a foundation for developing the advanced model, equations were formulated for an improved model incorporating separate gas and solids temperatures, but not incorporating the detailed coal reaction chemistry submodels or detailed compositions for bed hydrodynamics. A preliminary review of effective transport properties for fixed beds was also completed for the advanced model.
Revised User's Manual: 87-PCGC-2
Smoot, L.D.; Smith, P.J.; Brewster, B.S. and Baxter, L.L.
Advanced Combustion Engineering Research Center, 1988. Funded by US Department of Energy, Electric Power Research Institute, Consortium, and ACERC.
A two-dimensional, steady state model for describing a variety of reactive and non-reactive flows, including pulverized coal combustion and gasification, is presented. Recent code revisions and additions are described. The model, referred to as 87-PCGC-2, is applicable to cylindrical axi-symmetric systems. Turbulence is accounted for in both the fluid mechanics equations and the combustion scheme. Radiation from gases, wall and particles is taken into account using either a flux method or discrete ordinates methods. The particle phase is modeled in a Lagrangian framework, such that mean paths of particle groups are followed. Several multi-step coal devolatilization schemes are included along with a heterogeneous reaction scheme that allows for both diffusion and chemical reaction. Major gas-phase reactions are modeled assuming local instantaneous equilibrium, and thus the reaction rates are limited by the turbulent rate of mixing. A NOx finite rate chemistry submodel is included which integrates chemical kinetics and the statistics of the turbulence. The gas phase is described by elliptic partial differential equations that are solved by an iterative line-by-line technique. Under-relaxation is used to achieve numerical stability. The generalized nature of the model allows for calculation of isothermal fluid mechanics/gaseous combustion, droplet combustion, particulate combustion and various mixtures of the above, including combustion of coal-water and coal-oil slurries. Both combustion and gasification environments are permissible. User information and theory are presented, along with same problems.
Brewster, BS
1999
PDF Modeling of Lean Premixed Combustion Using In Situ Tabulated Chemistry
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, 119:233-252 (1999).
The velocity-composition probability density function (pdf) model coupled with a k-?-based mean flow computational fluid dynamics (CFD) model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a bluff-body, lean, premixed, methane-air combustor. Measured data [1,2] including velocity, temperature, and chemical species concentrations were used to evaluate the model. The chemistry calculations were performed with an in situ look-up tabulation method [3]. A reduced, 5-step chemical mechanism [4] for describing fuel oxidation, CO, and NO chemistry was used in the model. NO formation from thermal, N2O-intermediate, and prompt pathways was included in the 5-step mechanism. An axisymmetric, unstructured grid was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle equations. Predicted velocity and composition mean statistics were compared to measurements in the bluff-body combustor for a lean equivalence ratio of 0.59. The predictions of major species matched measured and calculated equilibrium values in the recirculation zone. Comparisons of mean CO throughout the combustor were always within an order of magnitude and showed marked improvements over past predictions. Maximum discrepancies between measured and predicted NO concentrations were between 5 and 7 ppm (~50%). The accessed composition space in this turbulent combustion simulation represented the values of species mole fraction and enthalpy for each fluid particle at each time step and was found to lie in a relatively small, uniquely shaped region that was dictated by the mixing, reaction, and heat transfer in the combustor. This accessed composition region was obtained in situ and required about 35 megabytes of storage once a steady state was reached. This memory requirement was more than three orders of magnitude less than would be needed in a standard, a priori table. The in situ tabulation approach allowed for technically correct and efficient chemical kinetic calculations by using the 5-step mechanism in this pdf-method-based, multidimensional combustor model.
1998
Stochastic Modeling of CO and NO in Premixed Methane Combustion
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, 113:135-146 (1998).
The ability to use reduced CH4-air chemical mechanisms to predict CO and NO emissions in premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with reduced 4-, 5-, and 9-step mechanisms and a detailed 276-step mechanism. NO emissions from thermal, N2O-intermediate, and prompt pathways were included in the 5-, 9-, and 276-step mechanisms. Molecular mixing was described with a deterministic, Interaction-by Exchange-with-the-Mean (IEM) submodel. Random selection and replacement (without repetition) of fluid particles were used to simulate through-flow. The evolution of mean and root mean square (rms) temperature, CO, and NO in the PaSR was accurately described with the 9-step mechanism over a wide range in mixing frequency and equivalence ratio. Also, the 9-step mechanism provided accurate instantaneous reaction rates and concentrations for a broad region of the accessed composition space in the PaSR. The 5-step mechanism performed less reliably than the 9-step mechanism at phi = 1.0 but performed similarly to the 9-step mechanism at phi = 0.65. The 4-step mechanism underpredicted mean CO values and overpredicted instantaneous temperature reaction rates, most likely due to its inferior parent mechanism, partial equilibrium assumption for OH, and unallowed dissociation of neglected radical species. The detailed and reduced mechanism predictions of the accessed composition space in the PaSR covered only a small fraction of the allowable composition space, thus facilitating the use of an efficient in situ chemical look-up table for multidimensional, pdf-method calculations.
1997
Stochastic Modeling of CO and NO in Premixed Methane Combustion
Cannon, S.M.; Brewster, B.S. and Smoot, L.D.
Combustion & Flame, (in press), 1997. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NO emission in premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with reduced 4-, 5-, and 9-step mechanisms and a detailed 276-step mechanism. NO emissions from thermal N2O-intermediate and prompt pathways were included in the 5-, 9- and 276-step mechanisms. Molecular mixing was described with a deterministic, Interaction-by-Exchange-with-the-Mean (IEM) submodel. Random selection and replacement (without repetition) of fluid particles was used to simulate through-flow. The evolution of mean and rms temperature, CO, and NO in the PaSR was accurately described with the 9-step mechanisms over a wide range in mixing frequency and equivalence ratio. Also, the 9-step mechanism provided accurate instantaneous reaction rates and concentrations for a broad region of the accessed composition space in the PaSR. The 5-step mechanism performed less reliably than the 9-step mechanism at phi = 1.0 but performed similarly to the 9-step mechanism at phi = 0.65. The 4-step mechanism underpredicted mean CO values and overpredicted instantaneous temperature reaction rates, most likely due to its inferior parent mechanism, partial equilibrium assumption for OH, and unallowed dissociation of neglected radical species. The detailed reduced mechanism predictions of the accessed composition space in the PaSR covered only a small fraction of the allowable composition space, thus facilitating the use of an efficient, in situ chemical look-up table in multi-dimensional, pdf-method calculations.
Comprehensive Model for Lean Premixed Combustion in Industrial Gas Turbines - Part I. Validation
Cannon, S.M.; Brewster, B.S.; Smoot, L.D.; Murray, R. and Hedman, P.O.
Presented at the Spring Meeting of the Western States Section/The Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy.
The velocity composition pdf model coupled with a mean flow CFD model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a swirling, lean premixed, methane-air combustor for which laser-based measurements of mean velocity and temperature were made. A flame was stabilized in this axi-symmetric, lab-scale, gas-turbine combustor (LSGTC. A reduced, 5-step chemical mechanism, for describing fuel oxidation and NO chemistry, was used in this LSGTC model. NO emissions from thermal, N2)-intermediate, and prompt pathways were described with this 5-step mechanism. The chemistry calculations were performed efficiently with and in-situ look-up table. An axi-symmetric, unstructured grid consisting of 2283 vertices and 4302 triangular elements was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle (~310,000 fluid particles) equations. Predicted velocity and composition statistics were compared to measurements in the LSGTC for lean equivalence ratios of 0.8 and 0.65. The comparisons of predicted mean velocity and temperature were reasonable good throughout the combustor. The location and magnitude of peak axial velocity was well represented by the model at near inlet regions, through the negative mean axial velocity in the internal recirculation zone was over-predicted. The predicted maximum mean temperature and the penetration zone of the cold unburned fluid were in reasonable agreement with the experimental data. Correct trends in CO and NO with equivalence ration were predicted with the model. The in situ tabulation method was used to represent the chemical kinetics in this axi-symmetric combustor without requiring significant CPU time and memory. The model is currently being applied to simulate 3-dimensional, gas-turbine combustor geometries and is described in a companion paper.
Comprehensive Model for Lean Premixed Combustion in Industrial Gas Turbines - Part II. Application
Meng, F.L.; Brewster, B.S. and Smoot, L.D.
Presented at the Spring Meeting of the Western States Section/The Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy.
A new comprehensive COmbustion Simulation MOdel for Gas Turbines (COSMO/GT) has been developed for simulating modern gas turbine combustors. The model includes the capability of simulating lean premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. In our earlier paper we extended the velocity-composition PDF approach to an unstructured grid platform for modeling two-dimensional, axisymmetric, lean premixed turbulent combustion in a lab-scale gas turbine combustor. In this paper, the extension of this PDF approach to a three-dimensional, unstructured grid is reported. The turbulence/chemistry interaction is modeled using the velocity-composition, Monte-Carlo PDF approach coupled with a five-step kinetic mechanism of methane and air for calculating CO and NO emissions. In order to increase the calculation speed of the PDF algorithm, in situ tabulation for chemical reaction and a zonal search method for locating particle positions are used. Validation of this model for and axisymmetric, lab-scale gas turbine combustor is described in a companion paper. Application of this model has been initiated by modeling lean, premixed combustion of natural gas and air in three-dimensional gas turbine combustors.
1996
Model Comparisons with Drop Tube Combustion Data for Various Devolatilization Submodels
Brewster, B.S.; Smoot, L.D. and Barthelson, S.H.
Energy & Fuels, 9:870-878, 1996. Funded by ACERC.
Predictions of a two-dimensional, axisymmetric combustion model, using various devolatilization submodel options, are compared with new experimental data from a near-laminar, drop-tube furnace. Included in the devolatilization submodels that were teste are the commonly used empirical one-and two-step models and a chemical, coal network model with parameters based on coal structure. The goals of this work were to evaluate the latter approach as compared with the simple, empirical approach usually used in such calculations and to assess the role of turbulence in a near-laminar reacting flow. Comparisons were made for carbon conversion, radially averaged oxygen and near-effluent NOX concentrations, for a range of coal types and equivalence ratios. The predictions quantify an ignition delay that is consistent with the measurements. Computations with the fundamental, chemical devolatilization submodel gave superior predictions of mass loss when the coal type was within the interpolation range of the submodel parameter database. Accuracy declined significantly when the coal type was outside the interpolation range. Inclusion of the effects of turbulence was required to account for the observations. Near effluent NO predictions with the chemical submodel agreed with measured NOX values to within an average of about 20 percent.
Modeling of Industrial Gas Turbine Combustors
Meng, F.L.; Farmer, J.R.; Brewster, B.S. and Smoot, L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section / The Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC.
A new model has been developed for simulating modern gas turbine combustors. The new model includes the capability of simulating lean, premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. The set of incompressible, steady state, Navier-Stokes equations is solved using a co-located, equal-order, control volume finite element method. The convection term is treated using the mass-weighted, skew upwind scheme, and the diffusion, pressure gradient, and source terms are interpolated linearly in each element. Turbulence is modeled using the kappa-epsilon model. Convective and radiative heat losses are modeled using a wall function method and a discrete ordinates method, respectively. The interaction between turbulence and chemistry is modeled using the velocity-composition Monte-Carlo PDF approach, coupled with a multiple-step reaction mechanism for methane and air. Validation of the code has been initiated by modeling lean, premixed combustion (Phi = 0.8) of natural gas and air in a laboratory-scale, gas turbine combustor with a simple, two-step kinetic mechanism for CH4-O2. Comparison with detailed measurements is forthcoming. Application to industrial gas turbine combustor components is also underway.
Prediction of CO and NOx in Lean Premixed Turbulent Combustion
Cannon, S.M.; Brewster, B.S. and Smoot L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section/The Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NOx emissions in lean premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with mathematically reduced 4-, 5- and 9-step mechanism and a detailed 276-step mechanism. NOx emission form thermal, N2O-intermediate, and prompt pathways were described with the 5-, and 9-step reduced mechanisms provided accurate instantaneous reaction rate calculations for a broad region of the accessed composition space in the PaSR. The 4-step mechanism and the partial equilibrium assumption for OH. Practicality of using the 5- and 9-step mechanisms in industrial, 3-dimensional calculations may require the use of a novel, in situ look-up table.
Prediction of CO and NOx in Lean Premixed Turbulent Combustion
Cannon, S.M.; Brewster, B.S. and Smoot L.D.
Proceedings of the Fall 1996 Meeting of the Western States Section/The Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NOx emissions in lean premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with mathematically reduced 4-, 5- and 9-step mechanism and a detailed 276-step mechanism. NOx emission form thermal, N2O-intermediate, and prompt pathways were described with the 5-, and 9-step reduced mechanisms provided accurate instantaneous reaction rate calculations for a broad region of the accessed composition space in the PaSR. The 4-step mechanism and the partial equilibrium assumption for OH. Practicality of using the 5- and 9-step mechanisms in industrial, 3-dimensional calculations may require the use of a novel, in situ look-up table.
1994
Fossil-Fuel Conversion - Measurement and Modeling
Solomon, P.R.; Serio, M.A.; Hamblen, D.G.; Smoot, L.D.; Brewster, B.S. and Radulovic, P.T.
Proceedings of the Coal-Fired Power Systems 94 - Advances in IGCC and PFBC Review Meeting, Morgantown, West Virginia, June 1994. Funded by US Department of Energy/Morgantown Energy Technology Center.
The main objective of this program is to understand the chemical and physical mechanisms in coal conversion processes and incorporate this technology for the purposes of development, evaluation in advanced coal conversion devices. To accomplish this objective, this program will: 1) provide critical data on the physical and chemical processes in fossil fuel gasifiers and combustors; 2) further develop a set of comprehensive codes; and 3) apply these codes to model various types of combustors and gasifiers (fixed-bed transport reactor, and fluidized-bed for coal and gas turbines for natural gas).
To expand the utilization of coal, it is necessary to reduce the technical and economic risks inherent in operating a feedstock which is highly variable and which sometimes exhibits unexpected and unwanted behavior. Reducing the risks can be achieved by establishing the technology to predict a coal's behavior in a process. This program is creating this predictive capability by merging technology developed at Advanced Fuel Research, Inc. (AFR) in predicting coal devolatilization behavior with technology developed at Brigham Young University (BYU) in comprehensive computer codes for modeling of entrained-bed and fixed-bed reactors and technology developed at the U.S. DOE-METC in comprehensive computer codes for fluidized-bed reactors. These advanced technologies will be further developed to provide: 1) a fixed-bed model capable of predicting combustion and gasification of large coal particles, 2) a transport reactor model, 3) a model for lean premixed combustion of natural gas, and 4) an improved fluidized-bed code with an advanced coal devolatilization chemistry submodel.
1993
Development and Application of an Acid Rain Precursor Model for Practical Furnaces
Smoot, L.D.; Boardman, R.D.; Brewster, B.S.; Hill, S.C. and Foli, A.K.
Energy & Fuels, 7 (6):786-795, 1993. Funded by ACERC.
Control of emissions of sulfur (SO2, SO3, H2S) and nitrogen (NO, NO2, N2O, HCN, NH3) pollutants from fossil-fuel-fired furnaces and gasifiers remains a vital worldwide requirement as the utilization of fossil fuels continues to increase. Development and refinement of a predictive model for these acid rain precursors (MARP) has reached the point where this technology can contribute to acid rain control. In this paper, model foundations and recent developments are summarized, including formation of thermal and fuel NOx and sorbent capture of sulfur oxides. The method includes global formation, capture, and destruction processes in turbulent, reacting, particle-laden flows. This submodel has been combined with comprehensive, generalized combustion models (PCGC-2, PCGC-3) that provide the required local properties for the combustion or gasification processes. The submodel has been applied to NOx formation in a full-scale (85 MWe), corner-fired utility boiler, where recent in situ NOx measurements were made, with variations in coal feedstock quality (including fuel N percentage) load-level and percentage excess air. Predictions are also made for in situ sorbent capture of sulfur pollutants in both combustion (fuel-lean, SO2), and gasification (fuel-rich, H2S) laboratory-scale reactors. Limitations of MARP are identified and work to improve the submodel is outlined.
Comprehensive Modeling
Brewster, B.S.; Hill, S.C.; Radulovic, P.T. and Smoot, L.D.
Chapter 8, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter treats comprehensive modeling of combustion and gasification systems. Entrained, fluidized and fixed bed models are considered. Single and multidimensional models are reviewed. Developing comprehensive computer models to help design combustors and gasifiers for clean and efficient utilization of coal and other fossil fuels is a primary objective of ACERC. Such models provide not only a framework for effectively integrating combustion-related technology from a wide array of disciplines, but a vehicle for transferring this technology to industry. In order to be useful, these models must satisfy at least three criteria: First, the input and output must be easily accessible (user-friendly graphics must play a role here). Second, the computer algorithms must be robust and computationally efficient. And third, the models must be thoroughly evaluated to demonstrate applicability to industrial processes and to justify confidence in their predictions. Developing and implementing user-friendly, robust, efficient, applicable, accurate models requires significant, on-going effort that is reviewed herein.
Structure of a Near-Laminar Coal Jet Flame
Brewster, B.S. and Smoot, L.D.
Energy & Fuels, 7 (6):884-890, 1993. Funded by US Department of Energy.
Flame data from a near-laminar coal jet have been compared with model predictions. Inclusion of gas turbulence with laminarization was necessary for adequately predicting the upper-flame and postflame regions and for predicting particle dispersion. Dispersion of gas and particles was insensitive to inlet turbulence intensity. Gas buoyancy induced radially inward flow that opposed particle dispersion. Gas temperature was predicted too high near the coal nozzle, perhaps due to neglecting finite-rate mixing of volatiles with the bulk gas and chemical kinetics effects. Single-particle burning effects were important in the flame zone, as evidenced by the sensitivity of particle temperature to direct enthalpy feedback from volatiles combustion. Particle burnout was insensitive to enthalpy feedback, heterogeneous CO2 formation, and chemistry/turbulence interaction.
User's Manual for 93-PCGC-2:Pulverized Coal Gasification and Combustion Model (2-Dimensional) with Generalized Coal Reactions Submodel FG-DVC
Brewster, B.S.; Boardman, R.D.; Huque, Z.; Berrondo, S.K.; Eaton, A.M.; Smoot, L.D.; Zhao, Y.; Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Charpenay, S.; Best, P.E. and Yu, Z.-Z.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. II, 1993. Funded by US Department of Energy and Morgantown Energy Technology Center.
A two-dimensional, steady-state model for describing a variety of reactive and non-reactive flows, including pulverized coal combustion and gasification, is presented. Recent code revisions and additions are described. The model, referred to as 93-PCGC-2, is applicable to cylindrical, axi-symmetric systems. Turbulence is accounted for in both the fluid mechanics equations and the combustion scheme. Radiation from gases, walls, and particles is taken into account using a discrete ordinates method. The particle phase is modeled in a Lagrangian framework, such that mean paths of particle groups are followed. A new coal-general devolatilization submodel (FG-DVC) with coal swelling and char reactivity submodels has been added. The heterogeneous reaction scheme allows for both diffusion and chemical reaction. Major gas-phase reactions are modeled assuming local instantaneous equilibrium, and thus the reaction rates are limited by the turbulent rate of mixing. A thermal and fuel NOx finite rate chemistry submodel is included which integrates chemical kinetics and the statistics of the turbulence. A sorbent injection submodel with sulfur capture is included. The gas phase is described by elliptic partial differential equations that are solved by an iterative line-by-line technique. Under-relaxation is used to achieve numerical stability. Both combustion and gasification environments are permissible. User information and theory are presented, along with sample problems.
Measurement and Modeling of Advanced Coal Conversion Processes
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
US Department of Energy/Morgantown Energy Technology Center/Advanced Fuel Research/Brigham Young University Final Contract Report, Vol. I, 1993. (Also presented at the Coal-fired power systems 93 Conference, Morgantown, WV, June 1993.) Funded by US Department of Energy and Morgantown Energy Technology Center. (This report is available from Advanced Fuel Research, Inc.)
This project included research in the following areas: (1) fundamental high-pressure reaction rate data; (2) large particle oxidation at high pressures; (3) SOx-NOx submodel development; (3) integration of advanced submodels into entrained-flow code, with evaluation and documentation; (4) comprehensive fixed-bed modeling, review, development, evaluation and implementation; (5) generalized fuels feedstock submodel; (6) application of generalized pulverized coal comprehensive code and (7) application of fixed-bed code.
1992
Modeling Sorbent Injection and Sulfur Capture in Pulverized Coal Combustion
Boardman, R.D.; Brewster, B.S.; Huque, Z.; Smoot, L.D. and Silcox, G.D.
Air Toxic Reduction and Combustion Modeling, 15:1-9, 1992. (Also presented at the ASME International Joint Power Generation Conference, Atlanta, GA, October 1992). Funded by Advanced Fuel Research and ACERC.
A computer model has been developed for predicting mixing and reactions of injected sorbent particles in pulverized coal combustors and gasifiers. A shrinking-core, grain model was used for sulfation. The model accounts for the effects of surface area, pore diffusion, diffusion through the product layer, chemical reaction, and reduction of the pore volume due to grain swelling. The submodel was evaluated for a fuel-lean case and for a fuel-rich case. Predictions were compared with limited experimental data (for the fuel-rich case). The results illustrate the model's capability for predicting the effectiveness of sulfur capture. The importance of sorbent particle properties was also investigated parametrically, and model limitations were identified.
Application of Coal-General, 2-D Combustion Model
Brewster, B.S.
Ninth Annual Pittsburgh Coal Conference, Pittsburgh, PA, October 1992. Funded by Advanced Fuel Research.
A 2-D combustion model with advanced submodels for coal reactions and pollutants was used to simulate a cyclone combustor. Predicted gas velocity, coal particle trajectories, burnout, and sulfur capture by injected sorbent are presented. Particle trajectories are predicted to be very sensitive to particle size. The predictions give insight into the effects of reactor L/D ratio, coal; and sorbent particle size distribution, and optimal slag tap location. Needed model improvements include accounting for particle rebounding, sorbent calcinations and sintering, and sorbent particle dynamics. A 3-D model is needed to investigate the effects of particle injection geometry.
Comprehensive Fixed-Bed Modeling, Review, Development, Evaluation, and Implementation
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
21st, 22nd, and 23rd Quarterly Reports for the US Department of Energy, 1992. Funded by US Department of Energy and Morgantown Energy Technology Center.
The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal, a feedstock whose variable and often unexpected behavior presents a significant challenge. This program is merging significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation is being implemented and the technology was expanded to fixed-bed reactors. The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model has been integrated with BYU's comprehensive two-dimensional reactor mode, PCGC-2, which is a widely used reactor simulation for combustion or gasification. The program includes: 1) validation of the submodels by comparison with laboratory data obtained in this program, 2) extensive validation of the modified comprehensive code by comparison of predicted results with data from bench-scale and process scale investigations of gasification, mild gasification and combustion of coal or coal-derived products in heat engines, and 3) development of well documented user friendly software applicable to a "workstation" environment.
1991
Measurements and Modeling of Advanced Coal Conversion Processes: Fixed-Bed Coal Gasification Modeling
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
Contractors Review Meeting, Morgantown, WV, August 1991. Funded by Morgantown Energy Technology Center.
The overall objective of this program is to understand the chemical and physical mechanisms in coal conversion processes and incorporate this knowledge in computer-aided reactor engineering technology for the purposes of development, evaluation, design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. To accomplish this objective, the study will: establish the mechanisms and rates of basic steps in coal conversion processes, incorporate this information into comprehensive computer models for coal conversion processes, evaluate these models, and apply them to gasification, mild gasification and combustion in heat engines.
Measurement and Modeling of Advanced Coal Conversion Processes
Solomon, P.R.; Hamblen, D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
5th Annual Report for the US Department of Energy, 1991. Funded by Morgantown Energy Technology Center.
The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal a feedstock whose variable and often unexpected behavior presents a significant challenge. This program will merge significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation will be implemented and the technology will be expanded to fixed-bed reactors.
The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model will be integrated with BYU's comprehensive two-dimensional reactor model, PCGC-2, which is currently the most widely used reactor simulation for combustion or gasification. The program includes: i) validation of the submodels by comparison with laboratory data obtained in this program, ii) extensive validation of the modified comprehensive code by comparison of predicted results with data from bench-scale and process scale investigations of gasification, mild gasification and combustion of coal or coal-derived products in heat engines, and iii) development of well documented user friendly software applicable to a "workstation" environment. Success in this program will be a major step in improving the predictive capabilities for coal conversion processes including: demonstrated accuracy and reliability and a generalized "first principles" treatment of coals based on readily obtained composition data. The progress during the fifth year of the program is summarized in the document.
1990
Structure of a Near-Laminar Coal Jet Flame
Brewster, B.S.; Smoot, L.D.; Solomon, P.R. and Markham, J.R.
Tenth Annual Gasification and Gas Stream Cleanup Systems Contractors Review Meeting, Morgantown, WV, 1990. (Also Presented at the Western States Section/The Combustion Institute, San Diego, CA, 1990). Funded by Morgantown Energy Technology Center and Advanced Fuel Research Co.
An advanced 2-D model for pulverized-coal combustion has been modified and applied to a laminar coal flame in a transparent wall reactor. Modifications were made to allow for the up-fired flow configuration, laminarization, and gas buoyancy. A laminarization extension to the k- turbulence model was incorporated. Particle dispersion is sensitive to laminarization and to the value of turbulent particle Schmidt number. Predicted particle velocity and residence time are sensitive to the inclusion of gas buoyancy, which increases the velocity in the center of the reactor and induces a radial, inward flow. Model predictions have been compared with flame measurements to evaluate the comprehensive model that incorporates an advanced devolatilization submodel. Predicted velocities of burning particles agree well with values determined from particle streaks on video recording. Good agreement was also obtained between measured and predicted particle burnout. Discrepancies between measured and predicted particle and gas temperature may be due to neglecting heterogeneous formation of CO2 and the variation of char reactivity with extent of burnout. Discrepancies between predicted bulk gas temperature and measured CO2 gas temperature in the ignition zone can also be explained by the fact that the combustion energy first heats the CO2 that subsequently heats the other gases. Soot decays more slowly than predicted from equilibrium concentrations of condensed carbon.
1989
Measurement and Prediction of Thermal and Fuel NOx
Boardman, R.D.; Smoot, L.D. and Brewster, B.S.
Western States Section, The Combustion Institute, Livermore, California, 1989. Funded by US Department of Energy through subcontract from Advanced Fuel Research Co., and ACERC (National Science Foundation and Associates and Affiliates).
A generalized NOx model is being developed to predict nitric oxide formation in practical combustors. The NOx model incorporates an extended global fuel-NO mechanism and the modified Zeldovich mechanism to predict thermal NO formation. The importance of coupling turbulence with the chemical kinetics for practical combustors is addressed. Thermal NO data for a turbulent gaseous diffusion flame (in a laboratory-scale furnace) are presented. The model is being validated using these previously unpublished data and other pulverized-coal combustion and gasification data from the literature.
1988
Treatment of Coal Devolatilization in Comprehensive Combustion Modeling
Brewster, B.S.; Baxter, L.L. and Smoot, L.D.
Energy & Fuels, 2, (4), 362-370, 1988. 9 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
Comprehensive combustion codes typically use simple empirical models to predict weight loss associated with coal devolatilization. Individual evolved species are not taken into account nor are the individual products of heterogeneous char reaction. The effects of all particle reactions are lumped into a single overall rate of weight loss, and coal off gas composition and heating value are assumed constant. More detailed devolatilization models that consider the evolution of individual species and predict both rate and composition of the volatiles are now available. These models use general kinetic parameters for each coal constituent that are nearly independent of rank. Such models provide a basis for predicting composition and heating value of the volatiles as a function of burnout and reactor conditions for a wide range of coals. This paper presents a generalized theory based on the existing coal gas mixture fraction model, which allows the variation of off gas composition and heating value to be taken into account in comprehensive code predictions. Results are presented for a swirling combustion case. Results illustrating code sensitivity to several thermal parameters affecting devolatilization and to turbulent fluctuations are also presented. This publication also relates directly to Thrust Area 4.
Predicted Effects of Coal Volatiles Composition in Turbulent Flames
Brewster, B.S. and Smoot, L.D.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 22 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
The predicted effects of turbulence on the mean gas properties in coal combustors have been shown previously to be significant (Smith and Fletcher, 1986; Brewster, et al., 1988). These effects have been incorporated in comprehensive models by the statistical, coal-gas mixture fraction method (Smoot and Smith, 1985), which is based on the scalar approach for gas diffusion flames. Previously, only a single progress variable has been used for tracking coal off gas, including all material originating in the coal and transferring to the gas during the reaction process. Simple weight-loss models for devolatilization have been adequate for this approach that assumes constant off gas composition. With recent technological advances, the incorporation of detailed devolatilization models into comprehensive codes has become a practical consideration. However, detailed models that predict varying off gas composition require improved and/or extended methods of accounting for the effects of turbulence/chemistry interactions for successful incorporation.
In a recent paper, Brewster et al. (1988) presented a generalized formulation of the coal-gas mixture fraction method which allows for an arbitrary number of progress variables, thus allowing each element, or group of elements that evolve at similar rates, to be tracked independently. Independence of the progress variables was assumed, although it would not be difficult to include correlation coefficients if they were known. Results were presented for a slightly fuel-lean, swirling combustion case to illustrate the method. Two progress variables were used to separately track coal volatiles and char off gas, and significant decreases in the size of the fuel-rich region and in coal burnout were noted. These differences were attributed to the enriched oxygen content and (apparently) decreased heating value of the early off gas in the case of two progress variables. In this paper, additional results with multiple progress variables tracking coal off gas are reported and discussed. Calculations using an alternative method of calculating char off gas enthalpy agree qualitatively with previous observations of the effects of tracking volatiles and char off gas separately in combustion. Similar calculations in an oxygen-brown, fuel-rich gasification case show relatively little effect. Even less effect is observed when hydrogen from the coal is tracked separately and all of the other elements are lumped together. The effect of tracking volatiles separately decreased when ultimate volatile yield was increased from 40 to 80 percent, and noticeable differences existed with 50 percent heat loss (uniform) from the reactor compared to no differences when the reactor was assumed to be adiabatic. See also 1-88-J09 which relates to this Thrust Area.
Numerical Model of a Moving-Bed Coal Reactor
Yi, S.C.; Smoot, L.D. and Brewster, B.S.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
A literature review of existing models for moving-bed coal gasifiers and combustors was conducted, and three available 2-D codes were installed and tested. Predictions and sensitivity analyses of the 2-D code developed by Washington University (Bhattacharya et al., 1986) were performed. Based on the review, the proposed features of an advanced model incorporating detailed coal chemistry submodels were identified. One major difference between the proposed model and the existing models is that the proposed model will have separate gas and solids temperatures. As a foundation for developing the advanced model, equations were formulated for an improved model incorporating separate gas and solids temperatures, but not incorporating the detailed coal reaction chemistry submodels or detailed compositions for bed hydrodynamics. A preliminary review of effective transport properties for fixed beds was also completed for the advanced model.
Revised User's Manual: 87-PCGC-2
Smoot, L.D.; Smith, P.J.; Brewster, B.S. and Baxter, L.L.
Advanced Combustion Engineering Research Center, 1988. Funded by US Department of Energy, Electric Power Research Institute, Consortium, and ACERC.
A two-dimensional, steady state model for describing a variety of reactive and non-reactive flows, including pulverized coal combustion and gasification, is presented. Recent code revisions and additions are described. The model, referred to as 87-PCGC-2, is applicable to cylindrical axi-symmetric systems. Turbulence is accounted for in both the fluid mechanics equations and the combustion scheme. Radiation from gases, wall and particles is taken into account using either a flux method or discrete ordinates methods. The particle phase is modeled in a Lagrangian framework, such that mean paths of particle groups are followed. Several multi-step coal devolatilization schemes are included along with a heterogeneous reaction scheme that allows for both diffusion and chemical reaction. Major gas-phase reactions are modeled assuming local instantaneous equilibrium, and thus the reaction rates are limited by the turbulent rate of mixing. A NOx finite rate chemistry submodel is included which integrates chemical kinetics and the statistics of the turbulence. The gas phase is described by elliptic partial differential equations that are solved by an iterative line-by-line technique. Under-relaxation is used to achieve numerical stability. The generalized nature of the model allows for calculation of isothermal fluid mechanics/gaseous combustion, droplet combustion, particulate combustion and various mixtures of the above, including combustion of coal-water and coal-oil slurries. Both combustion and gasification environments are permissible. User information and theory are presented, along with same problems.