Radiative heat transfer from a turbulent diffusion buoyant flame with mixing controlled combustion

Masliyah, J.H.; Steward, F.R.

doi:10.1016/0010-2180(69)90069-8

Cited by 20 publications

(5 citation statements)

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“…Theoretical considerations show that comparable HC flare temperatures may be as low as 1100 °C. 15,23 Detailed laboratory measurements of temperatures associated with a propane flame in calm winds showed them to bẽ 1000 °C. 10 These were observed to increase to ~1200 °C as winds and stack exit velocities increased.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and Observational Assessments of Flare Efficiencies

Leahey

Preston

Strosher³

2001

Journal of the Air & Waste Management Association

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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 CO 2 and H 2 O. 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, IMPLICATIONS Flares are used extensively to dispose of gaseous wastes. The usual assumption is that combustion processes associated with flares efficiently convert HCs and sulfur compounds to relatively innocuous gases such as CO 2 , SO 2 , and H 2 O. It has been shown, however, that these processes can be efficient only at low wind speeds because the size of the flare flame, which is an indicator of flame efficiency, decreases with increasing wind speed. Therefore, the flaring process could routinely result, during periods of moderate to high wind speeds, in appreciable quantities of products of incomplete combustion such as anthracene and benzo(a)pyrene, which can have adverse implications with respect to air quality. 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%.

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Section: Introductionmentioning

confidence: 99%

Theoretical and Observational Assessments of Flare Efficiencies

Leahey

Preston

Strosher³

2001

Journal of the Air & Waste Management Association

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“…Calculations of the radiant flux distribution around a radiating flame generally involve complex integration procedures and numerical techniques [2,3]. A mathematical model of free-burning fires [4] has MAXIMUM FIRE INTENSITY (W/cm2) Figure 6.…”

Section: Calculations Of Heat Fluxmentioning

confidence: 99%

Measurements of the behavior of incidental fires in a compartment

Fang¹

1975

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“…[1] For economy and extension of previous studies of buoyant plumes [13] [10][11][12][13]. No horizontal pressure variation exists between the flame and the surrounding air.…”

Section: Analysis Of the Behaviormentioning

confidence: 99%

“…Assumptions 1 to 3 are common to most of the mathematical analyses of buoyancy-controlled turbulent plumes [10,[13][14][15][16].…”

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confidence: 99%

“…The assumption that the gas mixture inside the flame plume the plume is a black body emitter [11] , the plume gas is considered as an optically transparent medium [24], that the radiation can be divided into lateral and vertical components [26 , 27], and the radiating gas is a gray medium and the radiative interchange within the flame can be neglected [10] Using tiie ideal gas law as the equation of state, the energyequation (11) can be rev/ritten as (12) The boundary conditions for these differential equations are a=o;>tc=^o,^^^o .^xr'^io and y = yo …”

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confidence: 99%

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Analysis of the behavior of a freely burning fire in a quiescent atmosphere

Fang¹

1973

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INTRODUCTIONNo horizontal pressure variation exists between the flame and the surrounding air.4.The distributions of the velocity, temperature, and concentration in the transverse direction can be represented by the shape of a "top-hat" profile. 5.The transverse momentum flux due to the entrainmcnt of ambient air is pro-portional to the local upv/ard mom.entum flux of the rising flame gas.6.Ambient air is of uniform density and temperature.7.The gaseous fuel, combustion products and aml'^ient air are perfect gases with identical values of temperature-independent specific heat. The molecular v/eight of the combustion products in the buoyant plume zone and the ambient air are equal.8.In the combustion zone, the combustible volatiles mix with the entrained oxygen and burn instantaneously. 9.Radiative heat transfer can be neglected. The off-center maximum tends to shift to the flame axis as the unburned fuel reacts and the turbulent flame develops.It can be expected that velocity and concentration profiles within the flame plume will be similar to the temperature distribution. Therefore a "top-hat" profile for the mean vertical temperature, velocity, and concentration distributions although over-simplified is a reasonable assumption.The assumption that the entrainment constant for a turbulent buoyant jet with a density differing from the ambient air is proportional to the square root of the ratio of ambient 6 density to the average density inside the jet has been supported experimentally [21] and derived theoretically [22].Most fires in the open are not sufficiently large enough to cause significant variation of the temperature and density of the ambient atmosphere. However, these non-uniformity effects can be included in a manner similar to that used for natural convection column above fires [23][24][25].The assumption that the gas mixture inside the flame plume the plume is a black body emitter [11] , the plume gas is considered as an optically transparent medium [24], that the radiation can be divided into lateral and vertical components [26 , 27], and the radiating gas is a gray medium and the radiative interchange within the flame can be neglected [10]

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Radiative heat transfer from a turbulent diffusion buoyant flame with mixing controlled combustion

Cited by 20 publications

References 12 publications

Theoretical and Observational Assessments of Flare Efficiencies

Theoretical and Observational Assessments of Flare Efficiencies

Measurements of the behavior of incidental fires in a compartment

Analysis of the behavior of a freely burning fire in a quiescent atmosphere

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