10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Size, Effective Density, Volatility, Morphology, and Internal Structure of Soot Particles Generated from Large-Scale Turbulent Diffusion Flames
MOHSEN KAZEMIMANESH, Ramin Dastanpour, Alberto Baldelli, Melina Jefferson, Alireza Moallemi, Kevin Thomson, Matthew Johnson, Steven Rogak, Jason S. Olfert, University of Alberta
Abstract Number: 1009 Working Group: Combustion
Abstract Flares in the oil and gas industry are an important source of particulate emissions. Global gas flaring volume was approximately 150 billion m3 in 2016; however, very little is known about the physical, chemical, and optical properties of particle emissions from flares. To study these properties, a turbulent diffusion flame was set up at Carleton University Lab-scale Flare Facility which allowed controlled experiments on flames up to approximately three meters tall at fuel gas flow rates up to ~250 SLPM (standard litres per minute at 0°C and 101.325 kPa). Size distribution, effective density, volatility, morphology, and internal structure of soot particles generated from large-scale turbulent diffusion flames were characterized under various fuel composition and exit velocity conditions. Three different burner sizes with a diameter of 38.1, 50.8, and 76.2 mm were used in this study. The fuel exit velocities at the burner tip were 0.5, 0.9, and 1.5 m/s and the fuel flow rates were adjusted accordingly for each burner size, which resulted in a range of flow rates from 60.5 to 246.2 SLPM. Three different fuel mixture compositions (light, medium, heavy) were tested which resembled Alberta flare gas composition. The fuel gas mixture had 6 components (i.e., C1 to C4 alkanes, carbon dioxide, and nitrogen) and the mole fraction of methane in the light, medium, and heavy composition was 0.925, 0.866, and 0.769, respectively.
Combustion products were diluted by the ambient air on the order of ~20:1 to ~120:1 as they were drawn in the collecting fume hood and insulated duct using a variable speed fan. Size distributions of soot particles were measured using a scanning mobility particle sizer (SMPS), sampling from the duct and after the sample was further diluted by a factor of ~10:1 using an ejector diluter. Mass-mobility relations and effective densities of soot particles were determined using a tandem arrangement of a differential mobility analyzer (DMA), a centrifugal particle mass analyzer (CPMA), and a condensation particle counter (CPC). The volatility of particles was studied by adding a catalytic stripper (denuder) between the DMA and the CPMA. Morphology and internal structure of soot particles were studied using transmission electron microscopy (TEM) and Raman spectroscopy, respectively.
Results showed that the total particle number per unit mass of fuel ranged from 1.64×1014 kg−1 fuel to 9.08×1014 kg−1 fuel corresponding to light fuel mixture burned in the 76.2 mm burner with exit velocity of ~0.9 m/s and heavy fuel mixture burned in the 50.8 mm burner with exit velocity of 0.5 m/s, respectively. Particle size distribution changed noticeably with the fuel mixture composition; i.e., the particle median diameter was 66, 82, and 92 nm for light, medium, and heavy mixtures, respectively. Mass-mobility and effective density results showed that the average mass-mobility relationship was in good agreement with previously reported values for the mass-mobility of particles from different combustion sources in the literature. The results also showed that the mass fraction of volatile coating on the soot particles was negligible. Previously developed relations between effective density and primary particle size work well for the soot particles of this study. Raman spectroscopy indicated similar nanostructure for the studied fuel compositions. It may be possible to use a simple morphology model for all the conditions investigated in this study.