(222bh) Oxy-Fuel Combustion Optical Flame Analysis and Characterization

Title:Oxy-Fuel Combustion Optical Flame Analysis and Characterization

Lead Presenter's Email: casey.carney@contr.netl.doe.gov
KeywordsCombustion Flame Analysis, Fossil Fuel, Heat Transfer, Oxy-Fuel

Oxy-Fuel Combustion Optical Flame Analysis and Characterization

C. S. Carney^1,2, R. Woodside¹, S. J. Gerdemann¹, D. Oryshchyn¹, T. Ochs¹

¹National Energy Technology Laboratory, 1450 Queen Ave SW, Albany, OR 97321

²URS Corporation, P.O. Box 1959, Albany, OR 97321-0521

            Oxy-fuel combustion uses conventional technology for pulverized coal combustion, generating a flue gas composed primarily of carbon dioxide and water.  While conventional air-fired coal combustion flame behavior is fairly well understood and optimized, the absence of nitrogen and consequent increase of carbon dioxide fraction and mass flow differences in oxy-fuel combustion results in differing flame behavior.  Two notable examples are flame temperature and heat transfer within the boiler radiant zone.  A unique suite of optical instrumentation devices has been designed for the purpose of oxy-fuel combustion flame study: two monochromators, four total radiometers, two fiber optic CCD spectrometers, and a video camera.  These instruments view the flame via optical ports mounted along the flame axis – some along the burner centerline, and some 16” below the centerline.  This system is capable of analyzing the following flame components: temperature, radiance, stability, morphology, and radical species.  The radiometric components of the system will tend to observe emitted radiation from the soot particles, which will be used as a proxy for the flame’s temperature characteristic.      

            The monochromator records irradiance vs. wavelength over the range of 800-5000 nm.  Average radiant particle temperature can be calculated by fitting the Planck blackbody radiation curve to the shape of the spectrum over an optimized wavelength range for scan time minimization.  The radiometers record total radiant flame intensity over the range of 200-7000 nm, can indicate flame oscillatory behavior, and are located along the burner centerline axis, allowing for a flame intensity profile along the flame length.  The CCD spectrometers provide instantaneous and continuous radiance vs. wavelength spectra in the range of 230-1100 nm.  CCD spectrometer data are applied to calculate flame temperatures in their viewing area using the three-color method (evaluating the radiance ratio at three wavelengths).  Flame radical species can be identified by these spectrometers, which are of use for combustion diagnostics.  Rapid scan times enable the spectrometers to also indicate oscillations in the flame.  Flame stability and morphology are monitored with a high speed video camera with a 90° field of view that has been customized for high temperature flame use. 

            This optical flame measurement system has been installed at the Jupiter Oxygen Burner Test Facility (15 MWth) in Hammond, IN.  The test facility also contains various non-optical devices that further aid flame characterization such as thermocouples installed in inter-tube webbing and “chordal” thermocouples which can be used to determine boiler tube heat flux.  Online flue gas compositional analysis records combustion-product volume-fraction composition at the boiler exit.  The optical analysis system was operational for both conventional air firing and oxy firing testing.  These results will be presented and are used both for flame characterization and comparison to existing computational fluid dynamics boiler simulations, including radiant zone temperature and heat transfer mapping.