Combustion Flame Speeds and Stability of Associated Natural Gas with High Concentrations of C₂–C₄ Alkanes

Abstract

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 C2–C4 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 (ϕ = 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 C2–C4 alkanes.

Numerical study on the effects of ozone addition on the development of laminar premixed flames and emissions for methane and propane in a co-flow configuration

“…As such, when the combustion is promoted by ozone, the flames predicted for CH4/3810O3 and CH4/6000O3 move closer to the burner rim and thus the heat lost to the burner is raised because of the increment of temperature gradient [48]. This indicates that the blow-off is retarded which then enhances the flame stability for CH4/3810O3 and CH4/6000O3, as compared to those of the methane [47].…”

“…This agrees with that found in the experiment [35], for which the addition of ozone decreases the stand-off distance and the subsequent flame becomes closer to the burner rim. Although the development of the stand-off distance depends on several factors such as mixture velocity, φ and temperature [45][46][47], one possible reason for such behaviour might be the acceleration of fuel oxidation due to the ozone addition since equivalent mean inlet velocities are specified for methane, CH4/3810O3 and CH4/6000O3. This in-turn transports the flames closer to the burner particularly for CH4/6000O3, as observed from the temperature profiles in Fig.…”

The State of the Art of Laminar Burning Velocities of H2-Enriched n-C4H10–Air Mixtures

“…Therefore, new solutions to avoid these accidents are needed. In this sense, experimental and numerical investigations have been conducted on n-butane-air flames to determine their global combustion parameters, including ignition delay times [6][7][8], propagation parameters (peak explosion pressures, explosion times, maximum rates of pressure increase, and deflagration indexes) [9][10][11], as well as the laminar burning velocities [8,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”