1997
Thrust Area 6: Model Evaluation Data & Process Strategies
Three-Dimensional Model of a Pulverized Coal Corner-Fired Utility Furnace and Comparisons with Local Furnace Data and Boiler Exhaust NOx
Hwang, Y.-L.
Three-Dimensional Model of a Pulverized Coal Corner-Fired Utility Furnace and Comparisons with Local Furnace Data and Boiler Exhaust NOx, Ph.D./BYU, August 1997. Advisor: Howell
Differential Mass and Energy Balances in the Flame Zone from a Practical Fuel Injector in a Technology Combustor
Warren, D.L. and Hedman, P.O.
Journal of Engineering for Gas Turbines and Power, 119:352-61(1997). Funded in part by ACERC.
This paper presents further analysis of experimental results from and Air Force program conducted by researchers at Brigham Young University (BYU), Wright-Patterson Air Force Base (WFAFB), and Pratt and Whitney Aircraft Co. (P&W) (Hedman et al. 1994a, 1995). These earlier investigations of the combustion of propane in a practical burner installed in a technology combustor used: (1) digitized images from video and still film photographs to document observed flame behavior as fuel equivalence ratio was varied; (2) sets of LDA data to quantify the velocity flow fields existing in the burner; (3) CARS measurements of gas temperature to determine the temperature field in the combustion zone, and to evaluate the magnitude of peak temperature; and (4) two-dimensional PLIF images of OH radical concentrations to document the instantaneous location of the flame reaction zones. This study has used the in situ velocity and temperature measurements from the earlier study, suitably interpolated, to determine local mass and energy balances on differential volume elements throughout the flame zone. The differential mass balance was generally within about ±10 percent with some notable exceptions near regions of very high shear and mixing. The local differential energy balance has qualitatively identified the regions of the flame where the major heat release is occurring, and has provided quantitative values on the rate of energy release (up to -400 kJ/m³s). The velocity field data have also been used to determine Lagrangian pathlines through the flame zone. The local velocity and temperature along selected pathlines have allowed temperature timelines to be determined. The temperature generally achieves its peak value, often near the adiabatic flame temperature, within about 10 ms. These temperature timelines, along with the quantitative heat release data, may provide a bases for evaluating kinetic combustion models.
Combustion Measurements in an Industrial Gas-Fired Flat-Glass Furnace
Newbold, J.; McQuay, M.Q. and Webb, B.W.
J. Inst. Energy, 70:71-81(1997). Funded by US Department of Energy and Ford.
Profiles of velocity, species concentration (O2, CO, and CO2), wall incident radiative heat flux and temperature are reported in the combustion space of a regenerative, side-port, 550 t/day, gas-fired flat-glass furnace. A region exists of fast-moving gases near the glass, with axial velocity components exceeding 20 m/s, and a large recirculation zone near the crown. Temperatures as high as 1985 K in the flame and as low as 1750 K in the recirculation zone are reported. A region of intense reaction is observed near the glass, with large concentration gradients and incomplete combustion even in the tail of the flame. Local incident radiant fluxes on the crown were nearly uniform spatially at a level of 680 kW/m². In the portnecks, flat inlet velocity profiles were measured with a magnitude of approximately 11 m/s. Significant variations were observed in the exhaust profiles of most measured variables. Large errors in exhaust mass balance suggest a complex, three-dimensional flow with recirculation zones along the side walls of the portnecks. A nominal preheat air temperature of 1420 K and a variation of exhaust temperatures between 1630 K and 1835 K were noted. O2 concentrations as high as 8.4% were measured at the exit, suggestion a bypass of oxygen-rich flow around the flame. CO2 concentrations were the highest near the batch, where glass reactions are the most intense.
Measuring and Modeling Combustion in Glass Melting Furnaces
Webb, B.W.
The Glass Researcher, 6:16-18(1997). Funded in part by ACERC.
As the glass industry relies heavily on the combustion of fossil fuels for its energy for melting and refining glass, small increases in combustion efficiency can result in major savings in energy costs. However, enhancements in the combustion process often result in higher pollutants in the exhaust. Prototype testing of new furnace technologies is both risky and cost-prohibitive at the industrial scale. The ability to predict the combustion process provides a viable alternative to physical prototyping in the exploration of new furnace combustion technologies.
Local Temperature Measuremtents in a Full-Scale Boiler with Overfire Air
Tree, D.R. and Webb, B.W.
Fuel, 76:1057-1066(1997). Funded by New York State Electric & Gas Corp. and ACERC.
Gas temperature and effluent NOx measurements were obtained in a full-scale (160 MWe) pulverized coal corner-fired utility boiler with separate overfire air. The measurements are the first of this kind in a full-scale boiler operated with overfire air and low-NOx burners. A test matrix of seven operating conditions was used to compare temperature and NOx with changes in overfire air, coal type, load and burner tilt. Peak temperatures were 1500-1600°C and occurred just above the top burner. The measurements detailed the profile of temperature through a traverse of a coal burner, close-coupled overfire air port and separate overfire port. The data in the near-burner and overfire air regions showed evidence of reduced swirl as overfire air was increased. Little difference was seen in the temperatures for two coals with volatile fractions of 28 and 36 wt%. Temperature changes were quantified in the overfire air region for changes in burner tilt and load. Temperature was approximately the same in the overfire air region as load was decreased, but increased in this region as the burners were tilted from +5° to -5°.
Experimental Measurements in the Brigham Young University Controlled Profile Reactor
Tree, D.R.; Black, D.L.; Rigby, J.R.; McQuay, M.Q. and Webb, B.W.
Progress in Energy and Combustion Science, (in press), 1997. Funded by ACERC.
Energy conversion of fossil fuels or waste products to electricity and heat through clean and efficient combustion processes continues to be an issue of international importance. The Controlled Profile Reactor (CPR) is a small-scale (0.2 -0.4 MW) combustion facility that has been used to obtain data for model validation, the testing of new combustion concepts, and the development of new combustion instrumentation. The CPR has a cylindrical, down-fired combustion chamber, 240 cm long and 80 cm in diameter. This review of the past ten years of research completed in the CPR includes a description of the reactor and instrumentation used, a summary of three experimental data sets which have been obtained in the reactor, and a description of novel tests and instrumentation. Measurements obtained include gas species, gas temperature, particle velocity, particle size, particle number density, particle-cloud temperature profiles, radiation and total heat flux to the wall, and wall temperatures. Species data include the measurement of CO, CO2, NO, NOx O2, NH3 and HCN. The three combustion studies included one with natural gas combustion in a swirling flow, and two pulverized-coal combustion studies involving Utah Blind Canyon and Pittsburgh #8 coals. Most but not all of the above measurements were obtained in each study. The second coal study involving the Pittsburgh #8 coal contained the most complete set of data and id described in detail in Section II of the paper. Novel combustion instrumentation includes the use of Coherent Anti-Stokes Raman Spectroscopy (CARS) to measure gas temperature. Novel combustion experiments include the measurement of NOx and burnout with coal-char blends. The measurements have led to an improved understanding of the combustion process and an understanding of the strengths and weaknesses associated with different aspects of comprehensive combustion models.
Detailed Species and Temperature Measurements in a Pulverized Coal Flame with Natural Gas Reburning
Nazeer, W.A.; Jackson, R.E. and Tree, D.R.
Presented at the Fall Meeting of the Western States Section/Combustion Institute, SCAQMD Headquarter, Diamond Bar, California, October 23-24, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
Gas composition and temperature profiles have been measured inside a 200 KW, entrained flow, pulverized coal, Controlled Profile Reactor (CPR) using reburning for NOx reduction. Reburning in the CPR was achieved by creating a primary reaction zone, a reburning zone with natural gas injection, and a tertiary zone with additional air injection. The primary reaction zone under oxidizing conditions inhibits the formation of most of the fuel NOx. The natural gas injection in the reburning zone forms fuel radicals under reducing conditions, which react with primary zone NOx to convert it to elemental nitrogen. Air added in the tertiary zone consumes the leftover reburning fuel. The NO, CO, CO2, NOx, O2, HCN and NH3 samples were collected with a water-cooled and water-quenched stainless steel probe and analyzed on a dry basis with online gas analyzers. The temperature data inside the CPR was obtained with a suction pyrometer using a S-type shielded thermocouple. Both the species and temperature data points were obtained at swirl setting of 0, 0.5, and 1.5 to select a baseline condition for the implementation of a natural gas reburning section inside the CPR. The 1.5 swirl condition was chosen as a baseline for the reburning experiments because it provided and increased residence time for reburning and produced lower primary zone NOx without reburning. This condition also produced peak NOx in an annular region, which appeared to be a good target for the reburning fuel injection. Reburning was studied over a range of residence times and reburning zone equivalence ratios to optimize for maximum NOx reduction in the flue gases. The increase in equivalence ratios of the reburning zone showed an increase in NOx reduction up to a maximum of 68.5% at an equivalence ratio of 1.28. The residence time in the reburning zone was varied by moving the tertiary air injector up and down axially. The increase in residence time in the reburning zone increase NOx reduction to a maximum of 68% when the tertiary air injector was at an axial location of 133 cm from the primary outlet. Further increases in the residence time, accomplished by moving the tertiary air injector to an axial location of 168 cm, did not change the percent of NOx reduction.
Comprehensive Combustion Code Predictions of the Flow Field for Pulverized Coal Combustion
Jackson, R.E.; Pickett, L.M. and Tree, D.R.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
Comprehensive combustion modeling predictions of a large laboratory (0.2 MW axisymmetric, pulverized coal reactor are compared with detailed velocity measurements. The reactor is down-fired and cylindrical with a radius of 75 cm and an axial length of 2.4 m. Three challenging areas for modeling are investigated, namely grid independence, inflow boundary conditions, and turbulence. The predictions are compared with LDA data obtained at radial profiles in the quarl and at various axial locations throughout the reactor. These velocity maps for the reactor were obtained at three swirl settings at an equivalence ratio of 0.9. Two readily available combustion CFD codes were used, FLUENT and PCGC-3. Proper grid resolution is shown to be particularly important in the flame region. Grid independence for the primary glow structures was achieved for the laboratory reactor. The gross characteristics of the CFD solutions are less sensitive to inflow BCs than expected. The standard kappa-epsilon two-equation model was compared to an RNG base kappa-epsilon model and a non-linear kappa-epsilon model.
LDA, Gas Species and Temperature Measurements in a Pulverized Coal Flame
Pickett, L.M.; Jackson, R.E. and Tree, D.R.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tangential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on velocity slop encountered when coal is used as a seed particle for LDA was performed. Detailed velocity measurements at the outlet plane of a geometrically identical burner were obtained for use as boundary conditions. Velocity data of this type is useful in understanding the nature of pulverized coal flames, particularly with regard to NOx formation, and in developing models for pulverized coal combustion. The reacting flow velocity measurements were obtained throughout the near burner region of the reactor for three swirl settings at an overall stoichiometric ratio of 1.1. The coal-flame velocity data was useful in characterizing the flame structure indicating a centerline flame at 0 swirl transitioning to a radially directed flame with a central recirculation zone at swirl settings of 0.5 and 1.5. The transition of the flame structure to a central recirculation zone was also seen at the burner exit plane in the non-reacting flow studies and was found to correlate with a decrease in measured effluent NOx. At the flow rates and accelerations experienced in this study, the coal particles were shown to have minimal velocity slip. The velocity measurements from this study in combination with gas species and temperature measurements to be reported elsewhere combine to make a rare and comprehensive data set suitable for comprehensive coal combustion modeling development.
Two-Color Transmittance Measurements in a Pulverized Coal Flame
Tree, D.R. and Haneberg, A.L.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by ACERC.
Temperature is one of the most important parameters used in characterizing flames. Soot causes significant radiation heat transfer in flames reducing the temperature and affecting flame heat transfer, flame stability and pollutant formation. A method is introduced for the measurement of soot volume fraction in coal flames using two-color extinction. The method relies on the optical properties of the relatively small soot particles to attenuate light more efficiently than the other larger coal, char and ash particles in the flame. Using a two-wavelength transmittance measurement, the soot's contribution to extinction can be isolated. Analysis of the error shows the technique to be accurate within 50% of the majority of the error coming from the uncertainty of the refractive index and the possibility of forward scattering contaminating the true transmittance measurement. Experimental result in a 0.2 MW, down-fired, pulverized coal reactor burning WYODAK, sub-bituminous coal showed no measurable soot at a stoichiometric ratio of 1.11. Under fuel rich conditions, soot volume fractions of 1 -3 x 10^-7 were observed near the burner outlet. The minimum measurement threshold of the method was estimated to be approximately 5.0 x 10^-8.
Gas Velocity Measurements in a Coal-Fired Furnace with Comparisons to PCGC-2 Productions
Brooks, B.H.
Gas Velocity Measurements in a Coal-Fired Furnace with Comparisons to PCGC-2 Productions, M.S./BYU, January 1997. Advisor: Cannon
1997
Thrust Area 6: Model Evaluation Data & Process Strategies
Three-Dimensional Model of a Pulverized Coal Corner-Fired Utility Furnace and Comparisons with Local Furnace Data and Boiler Exhaust NOx
Hwang, Y.-L.
Three-Dimensional Model of a Pulverized Coal Corner-Fired Utility Furnace and Comparisons with Local Furnace Data and Boiler Exhaust NOx, Ph.D./BYU, August 1997. Advisor: Howell
Differential Mass and Energy Balances in the Flame Zone from a Practical Fuel Injector in a Technology Combustor
Warren, D.L. and Hedman, P.O.
Journal of Engineering for Gas Turbines and Power, 119:352-61(1997). Funded in part by ACERC.
This paper presents further analysis of experimental results from and Air Force program conducted by researchers at Brigham Young University (BYU), Wright-Patterson Air Force Base (WFAFB), and Pratt and Whitney Aircraft Co. (P&W) (Hedman et al. 1994a, 1995). These earlier investigations of the combustion of propane in a practical burner installed in a technology combustor used: (1) digitized images from video and still film photographs to document observed flame behavior as fuel equivalence ratio was varied; (2) sets of LDA data to quantify the velocity flow fields existing in the burner; (3) CARS measurements of gas temperature to determine the temperature field in the combustion zone, and to evaluate the magnitude of peak temperature; and (4) two-dimensional PLIF images of OH radical concentrations to document the instantaneous location of the flame reaction zones. This study has used the in situ velocity and temperature measurements from the earlier study, suitably interpolated, to determine local mass and energy balances on differential volume elements throughout the flame zone. The differential mass balance was generally within about ±10 percent with some notable exceptions near regions of very high shear and mixing. The local differential energy balance has qualitatively identified the regions of the flame where the major heat release is occurring, and has provided quantitative values on the rate of energy release (up to -400 kJ/m³s). The velocity field data have also been used to determine Lagrangian pathlines through the flame zone. The local velocity and temperature along selected pathlines have allowed temperature timelines to be determined. The temperature generally achieves its peak value, often near the adiabatic flame temperature, within about 10 ms. These temperature timelines, along with the quantitative heat release data, may provide a bases for evaluating kinetic combustion models.
Combustion Measurements in an Industrial Gas-Fired Flat-Glass Furnace
Newbold, J.; McQuay, M.Q. and Webb, B.W.
J. Inst. Energy, 70:71-81(1997). Funded by US Department of Energy and Ford.
Profiles of velocity, species concentration (O2, CO, and CO2), wall incident radiative heat flux and temperature are reported in the combustion space of a regenerative, side-port, 550 t/day, gas-fired flat-glass furnace. A region exists of fast-moving gases near the glass, with axial velocity components exceeding 20 m/s, and a large recirculation zone near the crown. Temperatures as high as 1985 K in the flame and as low as 1750 K in the recirculation zone are reported. A region of intense reaction is observed near the glass, with large concentration gradients and incomplete combustion even in the tail of the flame. Local incident radiant fluxes on the crown were nearly uniform spatially at a level of 680 kW/m². In the portnecks, flat inlet velocity profiles were measured with a magnitude of approximately 11 m/s. Significant variations were observed in the exhaust profiles of most measured variables. Large errors in exhaust mass balance suggest a complex, three-dimensional flow with recirculation zones along the side walls of the portnecks. A nominal preheat air temperature of 1420 K and a variation of exhaust temperatures between 1630 K and 1835 K were noted. O2 concentrations as high as 8.4% were measured at the exit, suggestion a bypass of oxygen-rich flow around the flame. CO2 concentrations were the highest near the batch, where glass reactions are the most intense.
Measuring and Modeling Combustion in Glass Melting Furnaces
Webb, B.W.
The Glass Researcher, 6:16-18(1997). Funded in part by ACERC.
As the glass industry relies heavily on the combustion of fossil fuels for its energy for melting and refining glass, small increases in combustion efficiency can result in major savings in energy costs. However, enhancements in the combustion process often result in higher pollutants in the exhaust. Prototype testing of new furnace technologies is both risky and cost-prohibitive at the industrial scale. The ability to predict the combustion process provides a viable alternative to physical prototyping in the exploration of new furnace combustion technologies.
Local Temperature Measuremtents in a Full-Scale Boiler with Overfire Air
Tree, D.R. and Webb, B.W.
Fuel, 76:1057-1066(1997). Funded by New York State Electric & Gas Corp. and ACERC.
Gas temperature and effluent NOx measurements were obtained in a full-scale (160 MWe) pulverized coal corner-fired utility boiler with separate overfire air. The measurements are the first of this kind in a full-scale boiler operated with overfire air and low-NOx burners. A test matrix of seven operating conditions was used to compare temperature and NOx with changes in overfire air, coal type, load and burner tilt. Peak temperatures were 1500-1600°C and occurred just above the top burner. The measurements detailed the profile of temperature through a traverse of a coal burner, close-coupled overfire air port and separate overfire port. The data in the near-burner and overfire air regions showed evidence of reduced swirl as overfire air was increased. Little difference was seen in the temperatures for two coals with volatile fractions of 28 and 36 wt%. Temperature changes were quantified in the overfire air region for changes in burner tilt and load. Temperature was approximately the same in the overfire air region as load was decreased, but increased in this region as the burners were tilted from +5° to -5°.
Experimental Measurements in the Brigham Young University Controlled Profile Reactor
Tree, D.R.; Black, D.L.; Rigby, J.R.; McQuay, M.Q. and Webb, B.W.
Progress in Energy and Combustion Science, (in press), 1997. Funded by ACERC.
Energy conversion of fossil fuels or waste products to electricity and heat through clean and efficient combustion processes continues to be an issue of international importance. The Controlled Profile Reactor (CPR) is a small-scale (0.2 -0.4 MW) combustion facility that has been used to obtain data for model validation, the testing of new combustion concepts, and the development of new combustion instrumentation. The CPR has a cylindrical, down-fired combustion chamber, 240 cm long and 80 cm in diameter. This review of the past ten years of research completed in the CPR includes a description of the reactor and instrumentation used, a summary of three experimental data sets which have been obtained in the reactor, and a description of novel tests and instrumentation. Measurements obtained include gas species, gas temperature, particle velocity, particle size, particle number density, particle-cloud temperature profiles, radiation and total heat flux to the wall, and wall temperatures. Species data include the measurement of CO, CO2, NO, NOx O2, NH3 and HCN. The three combustion studies included one with natural gas combustion in a swirling flow, and two pulverized-coal combustion studies involving Utah Blind Canyon and Pittsburgh #8 coals. Most but not all of the above measurements were obtained in each study. The second coal study involving the Pittsburgh #8 coal contained the most complete set of data and id described in detail in Section II of the paper. Novel combustion instrumentation includes the use of Coherent Anti-Stokes Raman Spectroscopy (CARS) to measure gas temperature. Novel combustion experiments include the measurement of NOx and burnout with coal-char blends. The measurements have led to an improved understanding of the combustion process and an understanding of the strengths and weaknesses associated with different aspects of comprehensive combustion models.
Detailed Species and Temperature Measurements in a Pulverized Coal Flame with Natural Gas Reburning
Nazeer, W.A.; Jackson, R.E. and Tree, D.R.
Presented at the Fall Meeting of the Western States Section/Combustion Institute, SCAQMD Headquarter, Diamond Bar, California, October 23-24, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
Gas composition and temperature profiles have been measured inside a 200 KW, entrained flow, pulverized coal, Controlled Profile Reactor (CPR) using reburning for NOx reduction. Reburning in the CPR was achieved by creating a primary reaction zone, a reburning zone with natural gas injection, and a tertiary zone with additional air injection. The primary reaction zone under oxidizing conditions inhibits the formation of most of the fuel NOx. The natural gas injection in the reburning zone forms fuel radicals under reducing conditions, which react with primary zone NOx to convert it to elemental nitrogen. Air added in the tertiary zone consumes the leftover reburning fuel. The NO, CO, CO2, NOx, O2, HCN and NH3 samples were collected with a water-cooled and water-quenched stainless steel probe and analyzed on a dry basis with online gas analyzers. The temperature data inside the CPR was obtained with a suction pyrometer using a S-type shielded thermocouple. Both the species and temperature data points were obtained at swirl setting of 0, 0.5, and 1.5 to select a baseline condition for the implementation of a natural gas reburning section inside the CPR. The 1.5 swirl condition was chosen as a baseline for the reburning experiments because it provided and increased residence time for reburning and produced lower primary zone NOx without reburning. This condition also produced peak NOx in an annular region, which appeared to be a good target for the reburning fuel injection. Reburning was studied over a range of residence times and reburning zone equivalence ratios to optimize for maximum NOx reduction in the flue gases. The increase in equivalence ratios of the reburning zone showed an increase in NOx reduction up to a maximum of 68.5% at an equivalence ratio of 1.28. The residence time in the reburning zone was varied by moving the tertiary air injector up and down axially. The increase in residence time in the reburning zone increase NOx reduction to a maximum of 68% when the tertiary air injector was at an axial location of 133 cm from the primary outlet. Further increases in the residence time, accomplished by moving the tertiary air injector to an axial location of 168 cm, did not change the percent of NOx reduction.
Comprehensive Combustion Code Predictions of the Flow Field for Pulverized Coal Combustion
Jackson, R.E.; Pickett, L.M. and Tree, D.R.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
Comprehensive combustion modeling predictions of a large laboratory (0.2 MW axisymmetric, pulverized coal reactor are compared with detailed velocity measurements. The reactor is down-fired and cylindrical with a radius of 75 cm and an axial length of 2.4 m. Three challenging areas for modeling are investigated, namely grid independence, inflow boundary conditions, and turbulence. The predictions are compared with LDA data obtained at radial profiles in the quarl and at various axial locations throughout the reactor. These velocity maps for the reactor were obtained at three swirl settings at an equivalence ratio of 0.9. Two readily available combustion CFD codes were used, FLUENT and PCGC-3. Proper grid resolution is shown to be particularly important in the flame region. Grid independence for the primary glow structures was achieved for the laboratory reactor. The gross characteristics of the CFD solutions are less sensitive to inflow BCs than expected. The standard kappa-epsilon two-equation model was compared to an RNG base kappa-epsilon model and a non-linear kappa-epsilon model.
LDA, Gas Species and Temperature Measurements in a Pulverized Coal Flame
Pickett, L.M.; Jackson, R.E. and Tree, D.R.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy/University Coal Research and ACERC.
A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tangential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on velocity slop encountered when coal is used as a seed particle for LDA was performed. Detailed velocity measurements at the outlet plane of a geometrically identical burner were obtained for use as boundary conditions. Velocity data of this type is useful in understanding the nature of pulverized coal flames, particularly with regard to NOx formation, and in developing models for pulverized coal combustion. The reacting flow velocity measurements were obtained throughout the near burner region of the reactor for three swirl settings at an overall stoichiometric ratio of 1.1. The coal-flame velocity data was useful in characterizing the flame structure indicating a centerline flame at 0 swirl transitioning to a radially directed flame with a central recirculation zone at swirl settings of 0.5 and 1.5. The transition of the flame structure to a central recirculation zone was also seen at the burner exit plane in the non-reacting flow studies and was found to correlate with a decrease in measured effluent NOx. At the flow rates and accelerations experienced in this study, the coal particles were shown to have minimal velocity slip. The velocity measurements from this study in combination with gas species and temperature measurements to be reported elsewhere combine to make a rare and comprehensive data set suitable for comprehensive coal combustion modeling development.
Two-Color Transmittance Measurements in a Pulverized Coal Flame
Tree, D.R. and Haneberg, A.L.
Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by ACERC.
Temperature is one of the most important parameters used in characterizing flames. Soot causes significant radiation heat transfer in flames reducing the temperature and affecting flame heat transfer, flame stability and pollutant formation. A method is introduced for the measurement of soot volume fraction in coal flames using two-color extinction. The method relies on the optical properties of the relatively small soot particles to attenuate light more efficiently than the other larger coal, char and ash particles in the flame. Using a two-wavelength transmittance measurement, the soot's contribution to extinction can be isolated. Analysis of the error shows the technique to be accurate within 50% of the majority of the error coming from the uncertainty of the refractive index and the possibility of forward scattering contaminating the true transmittance measurement. Experimental result in a 0.2 MW, down-fired, pulverized coal reactor burning WYODAK, sub-bituminous coal showed no measurable soot at a stoichiometric ratio of 1.11. Under fuel rich conditions, soot volume fractions of 1 -3 x 10^-7 were observed near the burner outlet. The minimum measurement threshold of the method was estimated to be approximately 5.0 x 10^-8.
Gas Velocity Measurements in a Coal-Fired Furnace with Comparisons to PCGC-2 Productions
Brooks, B.H.
Gas Velocity Measurements in a Coal-Fired Furnace with Comparisons to PCGC-2 Productions, M.S./BYU, January 1997. Advisor: Cannon