ACERC
Abstracts - 1986-1988 |
ACERC
Abstracts - 1986-1988 |
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Thrust Area 2: Fuels Minerals, Fouling and Slagging |
Blackham, A.U.
Fuel, 67, 27-35, 1988. 9 pgs. Funded by Utah Power and Light Co.
Use of lower than design grade coals can cause problems in furnaces and boilers due to increased ash deposits. A single-zone model has been developed to relate coal quality to thermal performance of pulverized, coal-fired power-generating boilers. The model, based on algebraic mass and energy balances and necessary auxiliary equations, estimates some of the required chemical and physical coal/ash properties. Three wall ash deposit parameters, thermal conductivity, emittance and thickness, have been determined by a sensitivity analysis to be critical to furnace performance and have been obtained by experimental procedures described herein. Data for ash properties are reported for Utah, Illinois and Western Kentucky bituminous coals. With these measured properties, the model has been used to predict effects of coal quality on furnace performance and to interpret changes in ash property data from a small-scale combustor to a large-scale utility boiler.
Submitted to Fuel, 1988. 22 pgs. Funded by Morgantown Energy Technology
Center.
This work summarizes several observations concerning the effects of pressure and oxygen-to-coal mass ratio on the fate of coal-sulfur during entrained gasification. A high-volatile bituminous coal was pulverized to a mass mean of near 50 mm. The coal was gasified with oxygen in a laboratory-scale entrained-flow gasifier. No steam was used. Test pressures were 1, 5 and 10 atm (100, 500, 1000 kPa). Oxygen-to-coal mass ratios between 0.60 (SR=0.30) and 1.10 (SR=0.56 were investigated. Gas-particulate samples were collected with a water-quenched probe from the gasifier chamber effluent stream. Measurements were made of the sulfur in the char particles and of the levels of H2 S, SO2, COS, and CS2 in the product gas.
Increasing pressure yielded a significant decrease (about 25%) in net conversion of coal sulfur. This decrease was evidenced by an increase in the sulfur content of the char samples, and by a decrease in total sulfur concentration in the gas phase. Gas species measurements showed that increased pressure yielded lower SO2 and CS2 concentration, but did not significantly affect H2S and COs concentrations. It was concluded that increased pressure shifted to distribution of sulfur among the gas phase species, yielding higher H2S and lower SO2 and CS2 concentrations. The increase in H2S was not seen in the measurements, because pressure also tended to increase the capture of H2S by char. Increasing oxygen-to-coal mass ratio increased sulfur conversion and SO2 and COs levels, while it decreased H2S and CS2 levels.
Accepted for publication Fuel, 1988. 33 pgs. Funded by Tennessee Valley
Authority.
Ash deposition tests were performed in a laboratory-scale, pulverized coal combustor with four different coals. These four coals, Kentucky No. 9, Kentucky No. 11, Illinois No. 5 and Illinois No. 6 had mass percent chlorine contents of 0.18, 0.10, 0.42 and 0.35 respectively. Five repetitive, one-hour firings were performed for each coal at a coal feed rate of 11 kg/hr. Ash samples were obtained from simulated waterwall and superheater probes, from an exhaust cyclone, and from a water-quenched char sample probe. Chlorine was found to release quickly from the coal to the gas phase. The amount of gas phase chlorine that concentrated on the ash collection surfaces was inversely dependent upon the temperature of the collection surface. The chlorine conversion rate from the char was equal to the carbon conversion rate for levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements, which were performed on samples from the waterwall and superheater probes showed no observable differences among the four coals tested. Obvious corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The one-hour firings were too short for many of the physical properties of the ash deposits to reflect the influence of metal corrosion. Emittance, ash sintering temperature compressive strength and shear strength of ash deposits were dependent on sample location.
Zaugg, S.D.; Blackham, A.U.;
Hedman, P.O. and Smoot, L.D.
Submitted to Fuel, 1988. Funded by Electric Power Research Institute.
A laboratory-scale pulverized coal combustor was used to determine the effects of secondary air swirl, stoichiometric ratio (O2/fuel), and coal type on the formation and reaction of sulfur pollutants (SO2, H2S, COs and CS2). Detailed local measurements within the reactor were obtained by analyzing solid-liquid-gas samples collected with a water-quenched probe. Increasing the stoichiometric ratio increased sulfur conversion and SO2 levels, and decreased H2S, COs, and CS2 levels. Swirl of secondary combustion air had a pronounced effect on the distribution of sulfur species formed at an O2-coal stoichiometric ratio of 0.87, but had very little effect at stoichiometric ratios of 0.57 and 1.17. Combustion of a bituminous coal produced more SO2 and less H2S, COs, and CS2 compared to a subbituminous coal.
Jamaluddin, A.S. and Smith,
P.J.
Western States Section, 1986, The Combustion Institute, Banff, Canada.
20 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.
Two radiative heat transfer codes, one based on the six-flux radiation model, and the other based on the S4 discrete ordinates model, have been developed. Both the radiation models approximate the angular variation of the radiation intensity by solving the radiation transport equation in a predetermined number of directions so that the angular integral is removed, resulting in differential equations which can be solved simultaneously with the differential equations of fluid flow, chemical reactions and heat transfer. The limited evaluation of these two models indicates that the six-flux model under-predicts the radiant heat fluxes by up to a factor of two, while the discrete ordinates model affords sufficiently accurate predictions for engineering heat transfer calculations.
Sowa, W.A.; Hedman, P.O.;
Smoot, L.D. and Blackham, A.U.
Western States Section, 1986, The Combustion Institute, Tucson, AZ. Also
accepted for publication in Fuel, 1988. 34 pgs. Funded by Tennessee Valley
Authority.
Ash deposition tests were performed in a modified pulverized coal combustor with four different coals: low chlorine Kentucky No. 9, and Kentucky No. 11, and high chlorine Illinois No. 5 and Illinois No. 6. The amount of coal available for testing differed markedly between coal types ranging from 100-1000 kg. per coal type. Several repeated one-hour combustion tests were performed for all four coals. Each firing consumed 15-25 kg. of coal. Ash deposition tests provided samples from simulated waterwall and superheater probes, and from an exhaust cyclone and a water-quenched char sample probe. Measured physical properties included, ash chemical analyses, proximate and elemental analyses of both raw coal and ash deposits, ash fusion temperature tests, ash sintering temperature tests, ash shear and compressive strength analyses, and ash thermal conductivity and emittance. Chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine condensed and concentrated on the waterwall collection surfaces. The amount of chlorine that condensed onto the ash collection surfaces was dependent on the temperature of the collection surface. The colder surfaces had the highest chlorine concentrations. Corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The carbon and chlorine conversion rate from the char appeared to be equal for carbon conversion levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements which were performed on samples from the waterwall and superheater probes showed no observable differences between the four coal types tested. The one-hour firings were probably too short for the ash deposits to reflect the influence of metal corrosion on the measured physical properties. Emittance, ash sintering temperature, compressive strength and shear strength were dependent on sample location.
Jones, M.L. and Benson,
S.A.
Proceedings of the Conference on the Effects of Coal Quality on Power Plants,
1987 Atlanta, Georgia. Funded by Coal Companies and Utility Companies.
Ash deposition is one of the greatest operational problems associated with the efficient utilization of low-rank coals in utility boilers. Also deposition can occur in two ways, slagging and fouling. For purposes of this discussion, fouling is defined as deposition in the convective section of the boiler and slagging as deposition in the convective pass, or fouling. The information required to better understand this process includes the mode of occurrence and abundance of the inorganic constituents, their reactions and transformations in the flame, mechanisms of ash transport and deposit growth, and interaction after deposition to form strong deposits. These issues are discussed in light of unique properties of the low-rank coals. Particular attention is paid to the mode of occurrence and abundance of the alkali and alkaline earth elements as well as their contribution to the liquid phase material critical to the development of strongly bonded ash deposits.
Jamaluddin, A.S. and Smith,
P.J.
Western States Section, 1987, The Combustion Institute, Provo, UT. 19
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.
Discrete ordinates solutions of the radiative transfer equation in two and three-dimensional rectangular enclosures containing absorbing-emitting-scattering media have been obtained using S2, S4, S6 and S8 approximations. Evaluation against exact analytical and numerical solutions show that while all of these approximations provide acceptable predictions of the radiation fluxes in two-dimensional enclosures, use of the higher order (higher than S4) approximations is not justified due to substantial increase in computational time and negligible improvement in the accuracy of the predictions. However, for three-dimensional enclosures, the S2 approximation is grossly in error. S4, S6 and S8 approximations predict wall heat fluxes and the temperatures of the medium accurately in these enclosures, but, once again, S4 approximation is shown to be adequate. A study of the sensitivity of the predicted net heat absorption by the walls to the dimensions of the system, and radiative properties of the medium and the surrounding walls, based on Fourier analysis technique, indicates that the predictions are more sensitive to the radiative properties than to the dimensions of the enclosure.
Smith, P.J.; Baxter, L.L.
and Jamaluddin, A.S.
AIChE Conference, 1988, New Orleans, LA. 15 pgs. All internal funding.
Heterogeneous heat transfer aspects strongly influence the performance of practical coal combustion systems since many of the subprocesses within the flame are highly temperature sensitive, and since the purpose of most furnaces is to extract energy from the flame. Coal combustion simulation or computer modeling permits investigation of the effect of various heat transfer mechanisms within flames on the many other simultaneous processes of turbulent fluid mechanics, coal conversion, gaseous reaction, etc. This paper examines two aspects of heat transfer on pulverized coal combustion processes: 1) the particle dominated radiation process and 2) the gas phase dominated turbulent convection processes. Comprehensive furnace modeling is used to study practical furnaces and the mechanisms are elucidated by comparing predicted results with experimental data from several coal and gas fired furnaces.
Jamaluddin, A.S. and Smith,
P.J.
Engineering Foundation Conference on Mineral Matter and Ash Deposition from
Coal, 1988, Santa Barbara, CA. 10 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 theoretical model has been developed to predict the rate of deposition of particulates from flowing turbulent gas-solid suspensions. The predictions of the model compare favorably with available experimental data. Incorporation of this technique into a comprehensive combustion code demonstrates promise for modeling slagging propensity in coal-fired furnaces.
Jamaluddin, A.S. and Smith,
P.J.
Proceedings of the 1988 National Heat Transfer Conference, 1, 227-232,
1988. 6 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.
The discrete-ordinates approximation is used to solve the radiative transfer equation in non-axisymmetric cylindrical enclosures containing absorbing-emitting and scattering media, with and without the temperature profile known a priori. Since neither detailed experimental data nor predictions from a zone or Monte-Carlo model for three-dimensional cylindrical enclosures is available, cylindrical equivalents of three-dimensional rectangular enclosures, for which zone model predictions of radiative transfer are available, are used in model evaluation. Limited evaluation of the model shows that the discrete-ordinates method provides acceptable predictions of radiative transfer in non-axisymmetric cylindrical enclosures.
McCollor, D.P.; Young, B.C.;
Jones, M.L. and Benson, S.A.
Accept for publication in the Twenty-Second International Symposium on Combustion,
1988. Funded by US Department of Energy and Pittsburgh Energy Technology Center.
A North Dakota lignite has been demineralized and selectively reloaded with calcium, potassium, and sodium cations by an ion-exchange process. Chars produced from the treated samples were burned in a laminar-flow reactor and single-particle temperatures were determined by optical pyrometry. Results show that sodium and potassium cations present in the chars have little effect on the char particle temperatures at low concentration (<5000 ppm). The results are consistent with carbon dioxide being produced at the char surface by catalytic action of the char mineral matter.
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