Black carbon particulate matter emission factors for buoyancy-driven associated gas flares

Abstract

Flaring is a technique used extensively in the oil and gas industry to burn unwanted flammable gases. Oxidation of the gas can preclude emissions of methane (a potent greenhouse gas); however, flaring creates other pollutant emissions such as particulate matter (PM) in the form of soot or black carbon (BC). Currently available PM emission factors for flares were reviewed and found to be questionably accurate, or based on measurements not directly relevant to open-atmosphere flares. In addition, most previous studies of soot emissions from turbulent diffusion flames considered alkene or alkyne based gaseous fuels, and few considered mixed fuels in detail and/or lower sooting propensity fuels such as methane, which is the predominant constituent of gas flared in the upstream oil and gas industry. Quantitative emission measurements were performed on laboratory-scale flares for a range of burner diameters, exit velocities, and fuel compositions. Drawing from established standards, a sampling protocol was developed that employed both gravimetric analysis of filter samples and real-time measurements of soot volume fraction using a laser-induced incandescence (LII) system. For the full range of conditions tested (burner inner diameter [ID] of 12.7-76.2 mm, exit velocity 0.1-2.2 m/sec, 4-and 6-component methane-based fuel mixtures representative of associated gas in the upstream oil industry), measured soot emission factors were less than 0.84 kg soot/10 3 m 3 fuel. A simple empirical relationship is presented to estimate the PM emission factor as a function of the fuel heating value for a range of conditions, which, although still limited, is an improvement over currently available emission factors.Implications: Despite the very significant volumes of gas flared globally and the requirement to report associated emissions in many jurisdictions of the world, a review of the very few existing particulate matter emission factors has revealed serious shortcomings sufficient to suggest that estimates of soot production from flares based on current emission factors should be interpreted with caution. New BC emissions data are presented for laboratory-scale flares in what are believed to be the first such experiments to consider fuel mixtures relevant to associated gas compositions. The empirical model developed from these data is an important step toward being able to better predict and manage BC emissions from flaring.

Global anthropogenic emissions of particulate matter including black carbon

“…These households often rely on fuel-based lighting, with the majority burning kerosene in wick-type lamps (Lam et al, 2012;Mills, 2005); their consumption was estimated at up to 25 billion litres of kerosene per year (Lam et al, 2012). Growing evidence suggests that these light sources pose risks to health (Pokhrel et al, 2010) and the environment (Lam et al, 2012), and improvements to lighting may provide numerous welfare benefits to households .…”

“…Some of the earlier published PM emission factors (about 2.6 g m −3 ) referred to landfill (CAPP, 2007) or refinery flares (US EPA, 1995) and are generally considered inappropriate. A new technique for quantitatively measuring soot emission rates in flare plumes under field conditions has been reported by the Carlton University group , and while their average BC emission factor of 0.51 g m −3 (McEwen and Johnson, 2012) considers representative fuel mixtures, their measurements were performed on laboratory-scale flares, which might underestimate real-world emissions. The first ECLIPSE datasets include flaring emissions calculated with one BC emission factor of 1.6 g m −3 gas flared, assuming that real-life flares perform much worse than laboratory measurements.…”

“…Reported specific kerosene consumption in kerosene lamps varied from 0.005 to 0.042 L h −1 (e.g. Mills, 2003;Pode, 2010) and we assumed 0.006 and 0.02 L h −1 for wick lamps and hurricane lanterns, respectively. Further, we assumed that each household will use three lamps for 6 h per day, whereas the share of hurricane lanterns is 20 % for South Asia and 50 % for other regions.…”

“…This modification was driven by the study highlighting the potentially high contribution of kerosene lamps to black carbon emissions (Lam et al, 2012). The emissions depend on what type of lamp is used, and for historical data we dis- tinguish between wick and hurricane lamps, with the former representing the majority (Lam et al, 2012;Mills, 2005). As a default, we assume 80 % kerosene wick lamps in South Asia and 50 % in other developing world regions.…”

A Generalized Sky-LOSA Method to Quantify Soot/Black Carbon Emission Rates in Atmospheric Plumes of Gas Flares

“…Furthermore, very limited emissions data are available for flares under controlled conditions and existing emission factor data used by many regulatory agencies to inventory flare generated PM are of questionable applicability (McEwen and Johnson 2012). However, a new technique for quantitatively measuring soot emission rates in flare plumes under field conditions has been recently demonstrated (Johnson et al 2010, which has potential to significantly improve understanding of flare generated PM emissions.…”