ACERC
Abstracts - 1989 |
ACERC
Abstracts - 1989 |
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Thrust Area 6: Model Evaluation Data and Process Strategies |
LaFollette, R.M.; Hedman,
P.O. and Smith, P.J.
Combust. Sci. and Tech., 66, 93-105, 1989. Funded by ACERC (National
Science Foundation and Associates and Affiliates).
Two-color optical pyrometers have been used to measure the temperature of reacting pulverized-coal particles. An analysis of such measurements was performed to determine the effect of several possible conditions on the measured temperature. The conditions investigated were the use of a single photo-multiplier to alternately measure the radiant emission at the two selected wavelengths, the presence of soot, light extinction, the choice of wavelengths used to compute the two-color temperature, and non-uniform particle clouds. A computer model of a one-dimensional coal particle cloud was written for this analysis. Results of calculations showed that artificially high temperatures can result if a pyrometer with a single photo detector is used to measure temperatures in a rapidly fluctuating flame. Emission by soot in the coal particle cloud caused unrealistically high temperature measurements. Light absorption by soot lowered the two-color temperature, but not enough to compensate for the rise in observed temperature caused by soot emission. When the wavelengths used are in the visible spectrum, the hotter particles are weighted much more heavily than when the wavelengths are in the infrared region. The use of Wein's Law, a valid approximation to Planck's Law in the visible spectrum, causes substantial error for longer wavelengths. Finally, the two-color temperature of a non-isothermal cloud was weighted most heavily by the hotter particles, depending upon the wavelengths used for the measurement. From this analysis important questions have been raised as to the validity of such measurements under transient conditions and during devolatilization.
Cope, R.F.; Smoot, L.D.
and Hedman, P.O.
Fuel, 68, 806-808, 1989. Funded by US Department of Energy (Morgantown
Energy Technology Center).
Elevated-pressure gasification tests were completed with North Dakota lignite, Wyoming subbituminous and Illinois No. 6 bituminous coals. Carbon conversion values obtained in theses tests were compared with those obtained with the same three coals at atmospheric pressure. Increased pressure produced greater increases in carbon conversion as coal rank decreased.
Lighty, J.S.; Silcox, G.D.;
Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Accepted for publication in Environ. Science Tech., 1989. Funded by the
Gas Research Institute, Dave Linz, Project Manager, National Science Foundation/Presidential
Young Investigators, ACERC (National Science Foundation and Associates and Affiliates),
the State of Utah, and US Department of Energy.
A major research effort has been initiated to characterize the rate-controlling processes associated with the evolution of hazardous materials from soils. A threefold experimental approach is being used in conjunction with computer modeling to analyze thermal desorption of contaminants. Phenomena occurring both inside particles (intraparticle) and with a bed of particles (interparticle) were studied.
The results obtained suggest that the most important process variables are local thermal environment and gas-phase contaminant concentration because the adsorption equilibrium characteristics of the contaminant/soil pair control the desorption of contaminant from a particle at a given temperature. A mass-transfer/desorption model, which assumes gas/solid equilibrium at all points and time, is proposed and the model was found to predict the measured temperature dependence.
Hancock, R.D.; Hedman, P.O.
and Kramer, S.K.
AIChE Annual Meeting, San Francisco, California, 1989. Funded by ACERC
(National Science Foundation and Associates and Affiliates).
Coherent anti-Stokes Raman Spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments. CARS has been applied to clean gas flames with great success, but very little research has been conducted in particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared to theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to the increased luminosity and enhanced background caused by particle and gas breakdown. The increased luminosity and breakdown alter the shape and intensity of the CARS signal, thus making analysis with unmodified versions of standard CARS fitting codes more complex.
CARS temperature and CO concentration measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CO concentration measurements deduced from the CO CARS spectra were less precise due to the difficulties of interpreting the CO CARS spectra in the presence of the enhanced background. Results generally agreed with thermochemical equilibrium combustion code calculations.
Boyack, K.W. and Hedman,
P.O.
Western States Section, The Combustion Institute, Livermore, California,
1989. (Also presented as a poster at the 1989 Gordon Conference on the Physics
and Chemistry of Laser Diagnostics in Combustion, Plymouth, New Hampshire).
Funded by ACERC (National Science Foundation and Associates and Affiliates).
The Coherent anti-Stokes Raman Scattering (CARS) technique has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, x, conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach was demonstrated by calibrations in CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms of fluctuations are attained in near stoichiometric mixtures and are estimated to be ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.
Measurements have been made using this instrument in turbulent nonpremixed jet flames of ~70% CO / 30% N2 with various amounts of H2 ranging from zero to 2.8%. Local extinction has been seen to occur as the H2 content is reduced, until the entire flame is extinguished. This extinction is thought to be due to insufficient radical concentrations, thus inhibiting chain-branching steps in the wet CO oxidation mechanism.
Cannon, J.N.; Kramer, S.K.;
Smoot, L.D. and Dahn, C.J.
Western States Section, The Combustion Institute, Pullman, Washington,
1989. Funded by ACERC (National Science Foundation and Associates and Affiliates)
and US Department of Energy.
Twenty-liter bomb tests have become a common method to evaluate safety implications involving pulverized coal (p.c.) in coalmines, coal power plant pulverizers and other equipment. However, only limited data are available for low rank coals. Further, some published bomb test results show more variation than is acceptable to many researchers which clouds credibility of the data. Often, significant variables are not controlled or reported adequately. The objective of this paper is to provide new data for low rank coals and illuminate the variables and effects that are significant.
Subbituminous coal from the Decker, Montana open pit mine was obtained from the mine face and immediately sealed in double-wall, plastic bags under nitrogen. Fifteen sets of 20-liter bomb tests with this coal were conducted to determine the effects of particle size, moisture, oxidation age and dust concentration on explosion characteristics. Mean particle size ranged from 3 to 50 mm; moisture ranged from 3 to 21%; low temperature oxidation age varied from mine-face fresh to 10 days. Dust concentrations ranged from 0.025 to 0.875 gm/liter. The test samples were obtained, stored, ground, classified and analyzed at this laboratory. The bomb tests were conducted by Safety Consulting Engineers Inc., of Chicago and included 20-liter bomb pressure-time traces. Maximum pressure varied between 95 and 135 psi and maximum pressure rise rate ranged from 2000 to 7000 psi/sec. The influence of coal sample storage length was examined through duplicate tests. Multivariate statistical regressions are used to extract information from the noted tests, clarifying the estimates of error for the data. Concentration and particle size have greater influence than moisture while oxidation age has very little influence.
The transient combustion processes during bomb tests are identified and the effects of the test variables are interpreted in light of these processes. Burning velocities are also estimated from various available theories and compared. Analytical methods show that the maximum pressure in the bomb is related to fuel concentration, fuel heating value and molecular weight of the product gases. Experimental results indicate that convective and radiant heat losses to the container wall and incomplete combustion significantly lower maximum pressure compared to predictions. In addition, initial turbulence in the bomb prior to ignition has a significant influence on observations. Requirements for controlling these variables in order to obtain consistent and repeatable test data from standard bomb tests are noted. The implication of the laboratory test results to full-scale explosions is also noted.
Nichols, K.M.; Hedman, P.O.
and Blackham, A.U.
1989 Joint Environmental Protection Agency/Electric Power Research Institute
Symposium on Stationary Combustion NOx Control,
San Francisco, California, 1989. Funded by ACERC (National Science Foundation
and Associates and Affiliates).
Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2, and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (SR = 0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of TFN decreased as pressure was increased. Neither TFN or N2 concentrations were affected by increasing residence time. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.
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