ACERC
Abstracts - 1992 |
ACERC
Abstracts - 1992 |
|
|
Thrust Area 6: Model Evaluation Data and Process Strategies |
Hancock, R.D.; Boyack, K.W.
and Hedman, P.O.
Chapter 15, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum
Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium
for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a diagnostic technique involving the use of high powered lasers to determine the temperature and concentration of the various major species found in combustion processes. This laser diagnostic technique allows in situ temperature and species concentration measurements to be obtained without disturbing the flame, as would most traditional thermocouples and sampling devices. Furthermore, there is no temperature limit associated with CARS because it is purely an optical technique.
CARS was first introduced by Taran and his co-workers at ONERA in France and was quickly recognized by other researchers throughout the world as a valuable diagnostic technique. Soon, numerous theoretical discussions, innovations, and practical applications of the CARS technique were introduced to the scientific community. CARS research has been implemented by various laboratories in the United States, Canada, England, France, Germany, Japan, and the Soviet Union.
Initially, CARS was applied to clean gas flames. However, as the instrument evolved, its diagnostic strengths were used to probe increasingly complex combustion environments. One such complex environment is that created by the introduction of particles into gas flames. Several researchers have studied such particle-laden flames and found them more difficult to probe, with the resulting CARS spectra more complex to analyze. These researchers have demonstrated that CARS measurements are possible in particle-laden flames.
Particle-laden flames are more difficult to probe because the particles attenuate the laser beams and can induce breakdown. Attenuation of the laser beams results in a loss of beam and signal strength. Breakdown alters the shape and intensity of the experimental spectra. The focus of this study was to develop methods by which consistent CARS measurements could be made on a regular basis in laboratory-scale particle-laden flames with coal loadings similar to those encountered in industrial burners.
This study extended the existing CARS instrument capability at Brigham Young University to a new laminar flame reactor that was designed to study flame speeds in pulverized coal flames. The facility modifications required the CARS laser beams to be transmitted over a 23-meter path length from the optical table to the reactor. The CARS signal was returned from the test chamber to the spectrometer with a fiber optic cable. The CARS signals were analyzed employing a modified version of the fitting code FTCARS from Sandia National Laboratories, using temperature and concentration libraries calculated with the CARS spectra code developed at Mississippi State University.
Sowa, W.A.; Hedman, P.O.;
Smoot, L.D. and Richards, D.O.
Fuel, 71(5):593-604, 1992. Funded by US Department of Energy, Morgantown
Energy Technology Center.
Three axisymmetric diffusion flame burners were designed and installed on a laboratory-scale, downfired, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. The gasifier performance was assessed by collecting space-resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas composition (CO, CO2, H2, H20 and CH4) and cold gas efficiency. Burner geometry affected carbon conversion, gas composition and cold gas efficiency. Each burner had unique flame structural characteristics that resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio. At 560 kPa, diffusion flame burner performance approached premixed flame performance. The results from this study suggest that it might be possible to design a diffusion burner that outperforms a fuel-oxidant premixing burner for some operating conditions due to its flame structure and its characteristic energy transfer to the chamber. Performance characteristics of diffusion burners correlated with system pressure, oxygen/coal ratio or steam/coal ratio cannot be generalized into trends representative of all diffusion flame burners.
Monson, C.R.; Germane, G.J.;
Blackham, A.U. and Smoot, L.D.
Fall Meeting of Western States Section/The Combustion Institute, Berkely,
CA, October 1992. Funded by US Department of Energy/Morgantown Energy Technology
Center through Advanced Fuel Research and ACERC.
Most of the coal currently being consumed is combusted at atmospheric pressure in utility furnaces, but several other processes are also being used and developed for either the direct combustion of coal or its conversion into other products. Many of these other processes, including coal gasification, operate at elevated pressure. While a great deal of research has been conducted on coal and char combustion at atmospheric pressure, elevated pressure char oxidation has largely been ignored. This paper describes the results obtained from char oxidation experiments at atmospheric and elevated pressures.
The experiments were carried out in a high-pressure, electrically heated drop tube reactor. A particle imaging system provided in situ, simultaneous measurement of individual particle temperature, size and velocity. Approximately 100 oxidation experiments were performed with two sizes (70 and 40 µm) of Utah and Pittsburgh bituminous coal chars at 1, 5, 10, and 15 atm total pressure. Reactor temperatures were varied between 1000 and 1500K with 5 to 21% oxygen in the bulk gas, resulting in average particle temperatures ranging from 1400 to 2100K and burnouts from 15 to 96%. Independently determined particle temperature and overall reaction rate allowed an internal check of the data consistency and provided insight into the products of combustion. Results from atmospheric pressure tests were shown to be consistent with results obtained by other researchers using the same coal. The chars burned in a reducing density and diameter mode in an intermediate regime between the kinetic and pore diffusion zones, irrespective to total pressure. Significant CO2 formation occurred at the particle surface at particle temperatures below about 1800K over the entire pressure range. Particle temperatures were strongly dependent on the oxygen and total pressures; increasing oxygen pressure at constant total pressure resulted in substantial increases in particle temperature, while increasing the total pressure at constant oxygen pressure led to substantial decreases in particle temperature. Increasing total pressure from 1 to 5 atm in an environment of constant gas composition led to modest increases in the reaction rate coefficients (based on the nth order rate equation) showed a large pressure dependence; both the activation energy and frequency factor decreased with increasing pressure. The results suggested that the empirical nth order rate equation is not valid at elevated pressures.
Pyper, D.K.; Blackham, S.;
Warren, D.; Hansen, L.; Christensen, J.; Haslam, J.; Germane, G.J. and Hedman,
P.O.
Fall Meeting of the Western States Section/Combustion Institute, Berkeley,
CA, October 1992. Funded by ACERC.
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 without the disturbing influence of a sample probe. CARS can be applied to dirty, luminous systems because it has a large signal to interference ratio due to high signal conversion efficiency and the coherent nature of the CARS spectral emission. CARS has been shown to be an effective means of determining the temperature and species concentrations in clean gas flames (Boyack, 1990). CARS measurements are more difficult to make in particle-laden 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.
The objectives of this study were to extend the capability at Brigham Young University (BYU) of making temperature measurements in the BYU-ACERC Controlled Profile Reactor (CPR) with gaseous and pulverized coal fuels, to demonstrate the ability of making reliable CARS temperature measurements in both clean and dirty flame, and to collect representative sets of data in a natural gas and in natural gas assisted coal flames. CARS temperatures were produced with a natural gas flame and with a mixture of natural gas and Utah Blind Canyon bituminous coal. The CARS signal in the natural gas-assisted coal flame showed the same resonant spectra from particle-induced gas breakdown as has been seen previously (Hancock, 1991 and 1992). The techniques of Hancock were used to account for the background spectra in analyzing the data from the coal flame. The coal concentration in the flame was limited by the CARS signal strength and the particle-induced gas breakdown signal strength at the detector.
CARS measurements were obtained at 4 cm intervals from -20 to +40 cm across the diameter of the 80 cm combustor. These radial data sets were collected at 10 different axial locations along the 2.5 m height of the reactor, giving a total of 160 separate locations. Two hundred single laser pulses were used at each location within the reactor to collect "single shot" temperature data, which allowed the calculation of local mean temperatures as well as probability density functions. These 200 single shots were repeated at least twice during the same test and several tests were duplicated. It was found that the temperature measurements were in good agreement during a single test, but the accuracy was in the order of ±100 K from test to test.
Warren, D.; Pyper, D.K.;
Blackham, S.; Christensen, J.; Hedman, P.O.; Goss, L.P.; Trump, D.; Sarka, B.;
Hsu, K.Y. and Roquemore, W.M.
Fall Meeting of the Western States Section/The Combustion Institute,
Berkeley, CA, October 1992. Funded by Wright-Patterson Air Force Base and Air
Force Office of Scientific Research.
This paper presents preliminary results of an Air Force Office of Scientific Research (AFOSR) program being conducted at Brigham Young University (BYU), Provo, Utah and at Wright-Patterson Air Force Base (WPAFB) under Summer Faculty and Research Initiation Programs. This study is part of an extensive research effort being carried out by the Fuels Combustion Group of the Aero Propulsion and Power Laboratory at Wright Patterson Air Force Base (APPL, WPAFB), Dayton, Ohio, in which simple and complex diffusion flames are being studied to better understand the fundamentals of gas turbine combustion. The program's long-term goal is to improve the design methodology of gas turbine combustors.
The work at BYU is being accomplished by the systematic study of a geometrically simple burner "designed and developed to specifically reproduce recirculation patterns and lean blow out (LBO) processes that occur in a real gas turbine combustor" (Sturgess, et al., 1990). There are two configurations used in the burner. The Task 100 burner uses a central fuel tube surrounded by a concentric air jet with a step expansion at the plane of discharge. The Task 150 burner has replaced the central fuel and air tubes with a double swirler injector from an actual Pratt-Whitney jet engine. Both configurations have been designed to be nearly axisymmetric and incorporate quartz windows to allow laser diagnostics. The burner is currently fueled by propane.
This paper contains a brief summary of work done at BYU and at Wright-Patterson Air Force base during the AFOSR summer faculty research programs. Intriguing flame structures have been visually characterized and captured in both still and video images with both the Task 100 and Task 150 configurations. Additional images of the flame and flow structures have been taken with laser sheet lighting, including Mie scattering and OH- florescence. These two-dimensional laser images have frozen structures missed with the visual observations due to the integrating nature of the eye and camera. LDA velocity maps have been collected over a variety of conditions, ranging from the relatively simple flow of the Task 150. This information not only yields velocity and turbulence data but will be used to obtain streamline functions as well. Both isothermal flow and combusting hot flow data have been collected. Limited CARS temperature data is compared in the paper LDA velocity maps and LIF image of OH-. Additional CARS temperature data are currently being collected at the test conditions of the LDA measurements and OH- images.
Cannon, J.N.; Webb, B.W.
and Bonin, M.P.
Heat Rate Improvement Conference, Birmingham, AL, November 1992. Funded
by Empire State Electric Energy Research Corp. and ACERC.
Brigham Young University/Advanced Combustion Engineering Research Center (BYU/ACERC) has been measuring combustion parameters in full-scale utility boilers with the intent of validating computer combustion models of coal burning processes throughout the boiler interior. Measurements were made in the burner region, fireball region and beyond the economizer. These measurements are spatially resolved for particle and gas temperature, particle size distribution, concentration and velocity, radiation and total wall flux, combustion gas products and pollutants (i.e. CO, CO2, O2, NO, and SOx) plus gas velocity and direction as well as turbulence intensity. In addition, in situ ash samples were collected.
Two bituminous coals were used in the test series conducted in the summer of 1991 at the New York State Gas and Electric (NYSGE) Goudey Station in Johnson City, New York. The test series variables were two different loads at two different excess air settings for two different coals and with pulverizer settings and burner tilt held constant. Tests were not conducted during soot and wall blowing periods. The two coals tested were both bituminous coals of similar heating value and ultimate analysis but differed in Hargrove Grindability Index (HGI), percent volatiles and ash properties.
The results indicate that most of the measured quantities could distinguish between the two relatively similar coals both in magnitude and location, highlighting the difference in burning characteristics of the two coals. These measured differences provide an explanation to why power plant operators respond to even similar coals as they do and gives credence to those actions. Seemingly small differences in a coal can make a significant difference in furnace behavior quantitatively. Internal boiler measurements of this kind are used to validate the computer combustion modeling programs.
Cannon, J.N.; Webb, B.W.
and Queiroz, M.
Advanced Combustion Engineering Research Center, Empire State Electrical
Energy Research Corp. Report, 1992. Funded by Empire State Electric Energy Research
Corp. and ACERC.
To validate the three-dimensional computer code under development by Brigham Young University, three-dimensional experimental data is needed. Experimental data from large-scale industrial furnaces is virtually nonexistent in the open literature. This study was directed to obtaining some of the needed experimental validation data that began with testing at NYSEG's Goudey Station in June 1989. Four operating parameters were varied during the 1989 Goudey tests: 1) load, 2) excess air, 3) coal fineness, and 4) burner tilt angle. The experimental data was obtained during two test sets. Twenty-six, 2-3 hour time blocks where operating parameters changed from test to test and a single, 24-hour period where operating parameters were held constant. Experimental data obtained during this study was taken by three teams. Results indicate that the data is internally consistent and accurate enough to validate the trends expected from the three-dimensional combustion code. Validation with the data will begin as soon as coal-qualified PCGC-3 comprehensive code is available from ACERC.
|