ACERC
Abstracts - 1986-1988 |
ACERC
Abstracts - 1986-1988 |
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Thrust Area 5: Comprehensive Model Development |
Suzuki, T.; Smoot, L.D.;
Fletcher, T.H. and Smith, P.J.
Combustion Science and Technology, 45, (3&4), 167-183, 1986. 17 pgs.
Funded by Brigham Young University and Kobe Steel Company, Japan.
The overall characteristics of high-intensity pulverized coal combustion have been predicted by a one-dimensional model. The mixing of the primary stream of pulverized coal and transport air with secondary combustion air was estimated by a growth angle of the primary jet. The coal particle burnout was strongly affected by the extent of devolatilization, which varies amount coals. The extent of devolatilization as characterized by variation in a devolatilization coefficient was correlated with either proximate volatiles percentage or H/C mass ratio of the virgin coal. The resulting comparisons of predictions with measurements for eight coal types and tree different combustors show that observed trends are generally predicted. The data used for these comparisons were obtained from a wide range of high-intensity combustion experiments. The proximate volatile matter in the virgin test coals ranged form 16 to 40 percent while the coal feed rate was varied from 12 to 290 kg/hr. Combustion air temperature varied from 297 to 1483 K while residence time ranged from 3 to 140 ms. Comparative results suggest that the predictive method can be useful in interpreting high intensity combustion test results.
Smith, J.D.; Smith, P.J.
and Hill, S.C.
Submitted for publication to Computer and Chem.Engineering, 1987. 35
pgs. Funded by ACERC Consortium: Babcock & Wilcox, Combustion Engineering,
Consol, Electric Power Research Institute, Empire State Electrical Energy Research
Corp., Foster Wheeler, Pittsburgh Energy Technology Center, Tennessee Valley
Authority, and Utah Power & Light.
An extensive parametric sensitivity study of a two-dimensional pulverized-fuel (pf) combustion model has been performed to investigate the effect of parametric uncertainty on model predictions. Results illustrate the dominant effect that error in coal devolatilization/oxidation parameters has on predicted burnout, Nox formation, local gas temperature, and coal-gas mixture fraction. Uncertainty in the turbulent particle dispersion parameters appear to have a secondary effect, while error in the particle-gas radiation parameters seems to have little impact on model predictions. Regions of the computational domain exhibiting sensitivity to specific parameters are identified. Specific parameter sensitivity implies the relative importance of various mechanisms in the overall process. Turbulent particle dispersion seems to be important early in the reactor with kinetic processes dominating at and following the predicted ignition point. Radiation appears to be of minor importance for the case under investigation. These results provide unique insight into the general pf combustion process. Specifically, they emphasize the need for a better methodology of predicting the overall volatiles yield. This implies additional understanding of the devolatilization/oxidation mechanism and its role in the overall pf combustion process. Although the results presented here are case specific, they provide unique insight into the overall pf combustion process and illustrate the effects that parameter uncertainty has on model predictions. This information provides fundamental direction for future comprehensive model development and focuses attention on pertinent experimental work to better quantify critical input parameters.
Lemieux, P.M. and Pershing,
D.W.
Submitted to Combustion Science & Technology, 1987. Funded by Westinghouse
and National Science Foundation/Presidential Young Investigators.
Previous experimental studies have indicated that rotary kilns may be suitable combustion systems to incinerate small quantities of off grade zirconium sponge produced during the manufacturing of zirconium for the nuclear industry. This paper describes a mathematical model of zirconium sponge combustion in a rotary kiln environment and specifically examines the use of the bed submodel to analyze detailed zirconium combustion data obtained previously in a rotary kiln simulator.
The results of this analysis indicated that the experimentally observed burning rates could be predicted within 25% based on available transport correlations and current understanding of zirconium combustion, without any adjustment of the physical parameters in the model both the experimental results and the model predictions indicated that the primary combustion parameters are the bulk oxygen concentration within the kiln and the local kiln bed temperature. Charge size was found to be less significant.
A detailed analysis of the theoretical predictions indicates that the zirconium sponge oxidation rate is controlled by three sequential processes (the convection of oxygen from the bulk gas to the top of the bed, the diffusion of oxygen through the bed to the particle surface, and the diffusion of oxygen through previously formed zirconium dioxide product to the unreacted zirconium metal). Under conditions typical of commercial rotary kiln operation all three of these resistances appear to be significant. Both the experimental data and the model suggest that the intrinsic chemical kinetics are fast and not controlling except during the first few minutes after the zirconium is charged. The model assumes that the zirconium oxide product layer increases until it reaches a maximum value after which it remains constant due to continuous formation and abrasion.
Brown, B.W.; Smoot, L.D.;
Smith, P.J. and Hedman, P.O.
AIChE Journal, 34, 3, 435-446, 1988. 12 pgs. Funding source by Morgantown
Energy Technology Center.
A detailed mathematical model is used to predict local and effluent properties within an axisymmetric, entrained-flow gasifier. Laboratory experiments were conducted to provide local properties for four coal types from a gasifier operating at near-atmospheric pressure. Effects of selected model parameters and test variables were examined and compared with measurements in most cases. The comparison of predictions and measurements provides the first evaluation of capabilities and limitations of a comprehensive model for entrained-flow gasifiers.
Stephenson, M.B.; Marchant,
G. and Crowfoot, T.
Accepted for publication in IEEE Computer Graphics and Applications,
1988. 17 pgs. Funded by ACERC (National Science Foundation and Associates and
Affiliates).
There are two major performance criteria for an engineering workstation, Central Processing Unit (CPU) performance and graphics performance. There are several standard CPU benchmarks (Dhrystone, Linpack, Whetstone, etc.), but engineering workstations that have nearly equal mips rating with these benchmarks perform very differently on real engineering problems. There are not standard graphics benchmarks.
The Engineering Computer Graphics Lab (ECGL) at Brigham Young University designed a set of benchmarks to evaluate the capabilities of high performance engineering workstations. The benchmarks were designed to evaluate the workstation's capacity to calculate and display solid finite element or finite difference data.
After running the ECGL's benchmarks on the several workstations, a cost/performance analysis was undertaken. This analysis was based on how many polygons/sec could be drawn per $10,000 invested.
Baxter, L.L.; Smith, P.J.
and Smoot, L.D.
Western States Section, 1986, The Combustion Institute, Banff, Canada.
17 pgs. Funded by ACERC Consortium: Babcock & Wilcox, Combustion Engineering,
Consol, Electric Power Research Institute, Empire State Electrical Energy Research
Corp., Foster Wheeler, Pittsburgh Energy Technology Center, Tennessee Valley
Authority, and Utah Power & Light.
Parameters for empirical devolatilization models are recommended for lignite and bituminous coals. These parameters were generated by combining optimization algorithms with rigorous particle and flow field modeling of experimental facilities.
PCGC-2, a comprehensive, axisymmetric, gasification and combustion code developed at the Brigham Young University Combustion Laboratory, was used to predict the velocity, temperature, and radiation fields of experimental apparatus used to collect devolatilization data. The effect of changing devolatilization models on these fields was neglected due to very low particle loadings. These fields were subsequently entered into a rigorous particle reaction model and the particle response to them was predicted.
A particle model predicted the trajectories, temperature, and reaction rates of coal particles in the flow fields described above. The particle model and its results are discussed. The particle model was coupled with an optimization algorithm to determine optimum parameters for the two-reaction devolatilization model.
Generalized reduced gradient (GRG) and sequential quadratic programming (SQP) methods were used in performing the optimization with OPTDES, an optimization program developed at Brigham Young University. The model parameters were optimized over six coal heat-up rates for each coal type. Statistical analyses of the residual sum of squares for the optimized two-reaction model revealed that there was no significant lack of fit of the data compared to the inherent variability of the data.
Smith, P.J.; Sowa, W.A.
and Hedman, P.O.
ASME Annual Meeting, 1986. 14 pgs. Funded by Morgantown Energy Technology
Center and Brigham Young University.
Comprehensive coal combustion (including gasification) models have received little to no use in furnace design applications due, in part, to their large computational burden when used in conjunction with some design optimization strategy. This paper presents a new design methodology that allows for the use of comprehensive coal combustion codes in design applications and provides a priori information on the cost of the optimization. A statistical response surface methodology is used to determine appropriate sample points from the design space at which the computations for the comprehensive code are performed. Statistical regression analysis is used to provide interpolating functions for the optimization package. The final design point is then checked with a final comprehensive code calculation.
The technique is demonstrated with simple examples for design of two injectors for an entrained coal gasifier and of a burner for a pulverized coal combustor. The three designs show the utility of the method as well as showing significantly different optima for different configurations. The importance of specifying operating conditions independently for different injectors or burners is demonstrated. The utility of comprehensive coal combustion codes as another design tool is demonstrated.
Smoot, L.D. and Smith, P.J.
ASME/JSME Thermal Engineering Joint Conference, 1987, Honolulu, Hawaii.
13 pgs. Funded by ACERC (National Science Foundation and Associates and Affiliates).
This paper provides a brief review of comprehensive modeling of combustion systems. The focus is on continuous, subsonic flow systems. Supersonic flows and intermittent or unsteady flows with combustion were not considered. Where condensed phases are present, the focus is further placed on entrained systems where particulate and droplet collisions or interactions through motion can be neglected. Gaseous, liquid, solid and slurry fuels were considered. A brief review of related literature is included. Model foundations, elements (submodels), requirements, and potential uses are summarized. Recent technical work of the authors or colleagues in turbulent fluid mechanics of swirling flows, radiation, and gas-phase reactions is summarized. Example predictions for selected cases are shown from several investigators, mostly with comparisons to measured properties. Future directions, research needs and plans are also identified.
Baxter, L.L. and Smith,
P.J.
Western States Section, 1987, The Combustion Institute, Honolulu, HI.
3 pgs. Funded by ACERC Consortium: Babcock & Wilcox, Combustion Engineering,
Consol, Electric Power Research Institute, Empire State Electrical Energy Research
Corp., Foster Wheeler, Pittsburgh Energy Technology Center, Tennessee Valley
Authority, and Utah Power & Light.
Classical assumptions about equilibrium conditions at phase interfaces during heat and/or mass transfer are shown to be approximations that can lead to errors in combustion environments. Specific illustrations involving droplet vaporization are given which show the nature and magnitude of the errors.
A method of relaxing these assumptions is discussed. Equations are developed from fundamental principles of physical chemistry to describe the actual conditions at interfaces. The corrections to the equilibrium assumptions depend on the rates of mass/heat transfer and physical constants that describe specific molecular behavior.
Computations illustrating the use of the nonequilibrium assumption reveal both the potentially large error associated with assuming equilibrium at the interfaces and the sensitivity of the predictions to the molecular parameters.
Bartholomew, C.H.
National AICHE Meeting, 1987, New York City. Funded by ACERC (National
Science Foundation and Associates and Affiliates), and US Department of Energy.
Basic and high technology industries are highly reliant upon an adequate supply of high-quality energy, the production of which depends upon combustion technology. The Advanced Combustion Engineering Research Center (ACERC) at Brigham Young University and the University of Utah conducts fundamental and experimental research leading to the development of advanced combustion technology. The new Center involves the cooperative efforts of two national laboratories, 24 industrial/research organizations located through the nation and two universities. Funding is provided by NSF, DOE, the State of Utah, 24 companies/laboratories, and the two universities. The principal objective of ACERC is to develop and implement advanced computer-aided design methods in combustion-related industry, with the emphasis on clean and efficient use of low-grade fuels. The approach is to integrate kinetic and mechanistic data, physical/chemical-fuels property data, and process-performance characteristics into comprehensive state-of-the-art computer models for use in the simulation, design and optimization of advanced combustion systems. The underlying philosophy is that a fundamental system approach applied to a few carefully selected systems can have wide application to many important combustion problems. Products of the Center include (1) new computer-aided-design combustion technology, (2) new understanding of combustion mechanisms and their relation to fuel properties, and (3) students educated in a fundamental of combustion engineering who can solve a wide range of problems. The heart of the Center's research program consists of 21 research projects at Brigham Young University and the University of Utah which are focused into six thrust areas: (1) comprehensive model development, (2) fuel characterization and reaction mechanisms, (3) fuel minerals, fouling, and slagging, (4) mechanisms of pollutant formation and hazardous-waste incineration, (5) process characterization/model evaluation, and (6) advanced combustion concepts. Examples of ongoing projects include NMR, mass spectrometry, and chromatographic studies of the products of coal devolatilization; reactor and surface studies of chars; development of pollutant submodels for sulfur dioxide removal by dry sorbent injection; development of a comprehensive 3D model for pulverized coal combustion; and CARS laser studies of pulverized coal combustion. Basic features of the presently used 2D model and plans for development of a new 3D model are discussed.
Gillis, P.A. and Smith,
P.J.
Western States Section, 1988, The Combustion Institute, Salt Lake City,
UT. 12 pgs. Funded by ACERC Consortium: Babcock & Wilcox, Combustion Engineering,
Consol, Electric Power Research Institute, Empire State Electrical Energy Research
Corp., Foster Wheeler, Pittsburgh Energy Technology Center, Tennessee Valley
Authority, and Utah Power & Light.
A three-dimensional non-reacting flow model has been developed for predicting flow inside industrial furnace configurations. The code uses the SIMPLE algorithm to couple the Navier-Stokes equations and solves the resulting matrices with a vectorized Thomas algorithm. Model predictions have been compared with experimental data in cross-fired furnace geometry. The k-e turbulence model produced significantly superior data agreement than the simpler turbulence models. The effect of inlet condition variation and grid resolution were demonstrated. It was also shown that fine grid spacing is needed to resolve localized large-scale vortex structure.
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.
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.
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