ACERC
Abstracts - 1997 |
ACERC
Abstracts - 1997 |
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Thrust Area 2: Fuels Minerals, Fouling and Slagging |
Spinti, J.
Formation of NOx During Char Oxidation, Ph.D./U
of U, September 1997. Advisor: Pershing
Wang, H. and Harb, J.N.
Progress in Energy and Combustion Science, 23:267-82(1997). Funded in
part by ACERC.
Traditional approaches to the prediction of the deposition behavior of a coal usually involve the use of empirical indices and ASTM ash fusion temperatures. These approaches, however, can give misleading results and are often unreliable. In recent years, considerable effort has been made in the development of models that overcome some of the deficiencies of the traditional approaches, as reviewed in the first part of this paper. In spite of advances, these models still fail to describe the effect of deposition on boiler operation. The second part of this paper documents the efforts in the Advanced Combustion Engineering Research Center (ACERC) to integrate an ash deposition model with a comprehensive 3D coal combustion model. An ash deposition submodel, which includes the effects of both ash chemistry and operating conditions on slagging deposits, has been incorporated into the comprehensive combustion coed, PCGC-3. The submodel includes a statistically based particle cloud model for determination of impaction rates of fly ash on boiler walls. The fraction of impacting particles that stick to the surface is determined from the physical characteristics (viscosity) of both the particles and the deposit surface. The model includes a description of deposit growth that approximates both the physical properties and chemistry of the deposit as a function of combustion conditions (operating conditions). A key feature of the model is its ability to account for the effect of deposition on operating conditions in the boiler. Simulations of deposition in both pilot-scale and utility-scale combustion facilities are reported in the paper.
Butala, S.; Medina, J.C.;
Bowerbank, C.R.; Lee, M.L.; Felt, S.A.; Taylor, T.Q.; Andrus, D.B.; Bartholomew,
C.H.; Yin, P. and Surdam, R.C.
Gas Research Institute, GRI-97/0213, July 1997. Funded in part by ACERC.
Coal seam reservoirs are important commercial sources of natural gas in the U.S. It is commonly assumed that coals function as self-sourced reservoirs for hydrocarbon gases formed by temperature-controlled thermolysis (cracking) of the bulk coal organic matter. However, this geologic process model may be an unreliable exploration guide. Artificial maturation results indicate that raw coal generates more hydrocarbon gas than demineralized coal. This difference suggests that mineral catalysis merits evaluation as a critical variable affecting hydrocarbon gas formation during coal maturation.
Kinetic modeling of temperature-controlled hydrocarbon thermolysis reactions using coal maturation geologic times and temperatures indicate that thermolysis reaction rates would be too slow to generate large, self-sourced coal seam natural gas deposits. By contrast, acid mineral, transition metal, and metal oxide mineral catalyzed reactions would occur at rates sufficiently fast under geologic time and temperature conditions to generate large quantities of natural gas. The unavailability of suitable benchmark coal reactivity data preclude assessment of whether catalytic reactions actually control hydrocarbon gas formation during coal maturation.
Fletcher, T.H.; Ma, J.;
Rigby, J.R.; Brown, A.L. and Webb, B.W.
Prog. Energy Combust. Sci., 23:283-301(1997). Funded by ACERC.
Soot is generated from coal when volatile matter, tar in particular, undergoes secondary reactions at high temperatures. A description of soot in coal flames allows better calculations of radiative transfer and temperatures in near-burner regions, which in turn allows more accurate predictions of NOx formation in coal-fired furnaces. Experiments are reviewed that examine the formation, agglomeration and properties of coal-derived soot, including pyrolysis experiments and combustion experiments. This review includes the types of experiments performed, the soot yields obtained, the size of the soot particles and agglomerates, the optical properties of soot, the relationship between coal-derived soot and soot form simple hydrocarbons, and attempts to model soot in coal flames.
Wang, H. and Harb, J.N.
Presented at the Engineering Foundation Conference, Kona, Hawaii, November
2-7, 1997. Funded in part by ACERC.
A critical element of any boiler model is the ability to address the influence of inorganic matter of ash on boiler operation and performance. This paper describes a mathematical model that has been integrated into the comprehensive combustion code PCGC-3, and used to predict the effect of slagging on boiler operation and performance. The model includes a description of particle transport, impaction, and sticking. In addition, it features the ability to estimate the heat flux and heat transfer properties through a deposit during deposit growth. Viscous flow sintering is the principal mechanism responsible for changes in the local properties of the deposit. Consequently, a transient description of sintering has been included in the model in order to estimate the properties as a function of time, particle size and composition at different positions in the deposit. An energy balance is used to determine deposit temperatures and the heat flux through the deposit. This balance accounts for variable physical properties and is solved iteratively with a predictor corrector technique at each time step during deposit growth. Validation of the integrated model has been accomplished by performing three-dimensional simulations of deposition in pilot-scale combustor at different operating conditions. Simulations of ash deposition during operation of a utility boiler are presented.
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