Flare stacks smokeless flaring

Flares ideally bum waste gas completely and smokelessly. Two types of flares are normally employed. The first is called the open flare, whereas the second is called the enclosed flare. The major components of a flare consist of the burner, stack. 

Elevated Flares See Flares for a general definition. The elevated flare, by the use of steam injection and effective tip design, operates as a smokeless combustion device. Flaring generally is of low luminosity up to about 20 % of maximum flaring load. Steam injection tends to introduce a source of noise to the operation, and a compromise between smoke elimination and noise is usually necessary. When adequately elevated (by means of a stack) this type of flare displays the best dispersion characteristics for malodorous and toxic combustion products. Visual and noise pollution often creates nuisance problems. Capital and operating costs tend to be high, and an appreciable plant area can be rendered unavailable for plant operations and equipment because of excessive radiant heat. 

Smokeless operation can generally be achieved, with essentially no noise or luminosity problems, provided that the design gas rate to the flare is not exceeded. However, since the flame is near ground level, dispersion of stack releases is poor and this may result in severe air pollution or hazard if the combustion products are toxic or in the event of flame-out. Capital and operating cost and maintenance requirements are high. 

When winterizing is required, the steam tracing and insulation should include the first 7.5 m of the flare stack above the vapor inlet and also in the case of a drum seal, the vapor line from the seal drum to the flare. Where steam injection to one of the smokeless tips, as shown in Figures 11 B and C is used, then the steam ring should remain outside the top of the flare tip (i.e., not internal). Where severe ambient conditions are encountered then it is recommended that the entire seal drum and flare be insulated in addition to steam tracing and open steam injection at base of flare. 

For non-smokeless flares (no steam injection) about 30% higher capacity can be allowed [59]. Therefore, the diameter of a non-smokeless flare stack is approximately (0.85) (diameter of the smokeless flare stack). 

Figure 7-71. Flare stack arrangement for smokeless burning and backflash protection with Fluidic Seal molecular seal. Steam can be injected into the flare to introduce air to the fuel by use of jets inside the stream and around the periphery. By permission, Straitz, J. F. Ill, Make the Flare Protect the Environment," Hydrocarbon Processing, Oct. 1977, p. 131.

Recent experience shows that stack diameters obtained by means of Figure 6-7 generally agree well with data for smokeless flare stacks. 

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