Theoretical and observational assessments of flare efficiencies.

Flaring of waste gases is a common practice in the processing of hydrocarbon (HC) materials. It is assumed that flaring achieves complete combustion with relatively innocuous byproducts such as CO2 and H2O. However, flaring is rarely successful in the attainment of complete combustion, because entrainment of air into the region of combusting gases restricts flame sizes to less than optimum values. The resulting flames are too small to dissipate the amount of heat associated with 100% combustion efficiency. Equations were employed to estimate flame lengths, areas, and volumes as functions of flare stack exit velocity, stoichiometric mixing ratio, and wind speed. Heats released as part of the combustion process were then estimated from a knowledge of the flame dimensions together with an assumed flame temperature of 1200 K. Combustion efficiencies were subsequently obtained by taking the ratio of estimated actual heat release values to those associated with 100% complete combustion. Results of the calculations showed that combustion efficiencies decreased rapidly as wind speed increased from 1 to 6 m/sec. As wind speeds increased beyond 6 m/sec, combustion efficiencies tended to level off at values between 10 and 15%. Propane and ethane tend to burn more efficiently than do methane or hydrogen sulfide because of their lower stoichiometric mixing ratios. Results of theoretical predictions were compared to nine values of local combustion efficiencies obtained as part of an observational study into flaring activity conducted by the Alberta Research Council (ARC). All values were obtained during wind speed conditions of less than 4 m/sec. There was generally good agreement between predicted and observed values. The mean and standard deviation of observed combustion efficiencies were 68 +/- 7%. Comparable predicted values were 69 +/- 7%.

The effect of bioaccumulated selenium on mortalities and deformities in the eggs, larvae, and fry of a wild population of cutthroat trout (Oncorhynchus clarki lewisi).

To determine if elevated concentrations of waterborne selenium (Se), caused by coal mining, in the Elk River in southeastern British Columbia, may be causing reproductive or teratogenic effects in wild cutthroat trout (Oncorhynchus clarki lewisi), fertilized eggs from exposed and reference fish were raised in the laboratory. Eggs from each female were reared separately and the percent mortalities and deformities were related to the selenium content of the eggs. Selenium concentrations in females from the exposed site were highest in the liver (36.6 +/- 22.5 microg/g dry weight, range: 18.3 to 114), followed by the eggs (21.0 +/- 18.3 microg/g, range: 8.7 to 81.3) and the muscle (12.5 +/- 7.7 microg/g, range: 6.7 to 41). Despite these elevated egg Se concentrations, there was no significant effect on fertilization; time to hatch; percent hatch; or egg, larvae, and fry deformities or mortalities. Reproductive failure and embryonic terata have been reported at much lower egg Se concentrations in other fish species. The lack of any toxic response in this study may be due to an evolved tolerance to higher tissue Se concentrations in a population of fish living in a seleniferous river system.

Characterization of emissions from diffusion flare systems.

Emissions from flares typical of those found at oil-field battery sites in Alberta, Canada, were investigated to determine the degree to which the flared gases were burned and to characterize the products of combustion in the emissions. The study consisted of laboratory, pilot-scale, and field-scale investigations. Combustion of all hydrocarbon fuels in both laboratory and pilot-scale tests produced a complex variety of hydrocarbon products within the flame, primarily by pyrolytic reactions. Acetylene, ethylene, benzene, styrene, ethynyl benzene, and naphthalene were some of the major constituents produced by conversion of more than 10% of the methane within the flames. The majority of the hydrocarbons produced within the flames of pure gas fuels were effectively destroyed in the outer combustion zone, resulting in combustion efficiencies greater than 98% as measured in the emissions. The addition of liquid hydrocarbon fuels or condensates to pure gas streams had the largest effect on impairing the ability of the resulting flame to destroy the pyrolytically produced hydrocarbons, as well as the original hydrocarbon fuels directed to the flare. Crosswinds were also found to reduce the combustion efficiency (CE) of the co-flowing gas/condensate flames by causing more unburned fuel and the pyrolytically produced hydrocarbons to escape into the emissions. Flaring of solution gas at oil-field battery sites was found to burn with an efficiency of 62-82%, depending on either how much fuel was directed to flare or how much liquid hydrocarbon was in the knockout drum. Benzene, styrene, ethynyl benzene, ethynyl-methyl benzenes, toluene, xylenes, acenaphthalene, biphenyl, and fluorene were, in most cases, the most abundant compounds found in any of the emissions examined in the field flare testing. The emissions from sour solution gas flaring also contained reduced sulfur compounds and thiophenes.