Combustion Flame Speeds and Stability of Associated Natural Gas with High Concentrations of C_2-C_4 Alkanes

摘要

Associated gas worth of tens of billions of dollars is flared annually during oil and gas production, which leads to resource waste and environmental issues. The combustion characteristics of associated gas mixtures with high concentrations of C-2-C-4 hydrocarbons, sometimes called high-BTU gases, were examined in this study. Specifically, adiabatic laminar flame speeds and combustion stability, including critical heat loss at extinction, were quantified for a range of associated gas mixtures. The study used a porous plug burner facility for stabilization of premixed, laminar flat flames with measured heat loss from the flames. Standoff distances of associated gas flames were measured using CH* chemiluminescence for validation of the technique by comparison with numerical simulations and analytical modeling, and standoff distance was used to determine stable operating points. Laminar flame speeds of the major component gases (methane, ethane, propane, and butane) and three associated gas mixtures from the Bakken gas field in North Dakota were investigated at lean to mildly rich equivalence ratios (phi = 0.7-1.1). Numerical simulations were performed using USC II and Aramco 1.3 mechanisms for comparison of numerical and experimental laminar flame speeds of component and associated gas mixtures. Additionally, a flame speed correlation was introduced to model the flame speeds of these quaternary gas mixtures. Finally, a heat loss ratio was defined through comparison of heat loss and burner firing rate, and critical heat loss ratios were identified where these associated gas mixtures become unstable and extinguish. Results are discussed in the context of utilization of associated gas with high concentrations of C-2-C-4 alkanes.