Self-consistent estimates of emission factors of carboncontaining pollutants from a typical gas flare

Abstract

This study proposes an approach for estimating the emission of soot, carbon monoxide (CO) and carbondioxide (CO ) from a typical gas flare. The estimations depend on the quantity and varying composition of the 2 natural gas, flame dynamics (represented by the fire Froude number, Fr ) and the equivalence ratio, f, of the fuel- f air mixture. Soot emission estimates are presented as a function of fire Froude number for gases used in labbased  test in order to validate the scheme and for two real-world fuel gas compositions. The mass-weighted carbon-hydrogen ratio (C:H) of the fuel gas compositions are 0.25 and 0.29 which are two extreme cases in terms of density. The soot yield of the lab-based test case was scaled up to estimate the soot yield of a full scale flare using the Richardson number as the scaling parameter. When all other variables are held constant at values characteristics of real-world flares, a difference of 16 % in the fuel-gas density, as indicated by the carbonhydrogen ratio, results in an increase of the emission factors (EF) of soot, CO and CO by factors of ~3, ~1.4 2 3 and ~1.7, measured in g/m , respectively. For both fuel gas compositions, the ratio of EF to EF at the fuel- soot CO lean region f < 1) is higher. The ratio lies in the range 0.031 – 0.13 and 0.0012 – 0.0055 for the fuel-lean (f < 1) and fuel-rich (f > 1) regions, respectively. The approach proposed and results obtained may be adopted to generate emissions inventories of emission species associated with gas flaring on regional and global scales.

Keywords: gas flaring; soot; natural gas; emission factor; black carbon; equivalence ratio