Theoretical and Observational Assessments Of Flare Efficiencies

摘要

Flaring of waste gases is a common practice in the processing of hydrocarbon materials. It isrnassumed that flaring achieves complete combustion with relatively innocuous by-products such asrncarbon dioxide and water. Flaring, however, is rarely successful in the attainment of completerncombustion. This is because entrainment of air into the region of combusting gases restricts flamernsizes to less than optimum values. Resulting flames are too small to dissipate the amount of heatrnassociated with 100 percent combustion efficiency.rnEquations developed by Leahey and Schroeder were employed to estimate flame lengths, areas andrnvolumes as functions of flare stack exit velocity, stoichiometric mixing ratio and wind speed. Heatsrnreleased as part of the combustion process were then estimated from a knowledge of the flamerndimensions together with an assumed flame temperature of 1200 K. Combustion efficiencies werernsubsequently obtained by taking the ratio of estimated actual heat release values to those associatedrnwith 100 percent complete combustion.rnResults of the calculations showed that combustion efficiency decreases rapidly as wind speedrnincreases from 1 to 6 m s~(-1). As wind speeds increase beyond 6 m s~(-1) combustion efficiencies tend tornlevel off at values between 10 to 15 percent. Propane and ethane tend to burn more efficiently thanrndo methane or hydrogen sulphide.rnResults of theoretical predictions were compared to nine values of local combustion efficienciesrnobtained as part of an observational study into flaring activity conducted by the Alberta ResearchrnCouncil. All values were obtained during wind speed conditions of less than 4 m s~(-1). There wasrngood agreement between predicted and observed values. The mean and standard deviation ofrnobserved combustion efficiencies were 68 ± 7 percent. Comparable predicted values were 69 ± 7rnpercent.