Explosive Limits Flare

Some vent streams, such as light hydrocarbons, can be discharged directly to the atmosphere even though they are flammable and explosive. This can be done because the high-velocity discharge entrains sufficient air to lower the hydrocarbon concentration below the lower explosive limit (API RP 521, 1997). Toxic vapors must be sent to a flare or scrubber to render them harmless. Multiphase streams, such as those discharged as a result of a runaway reaction, for example, must first be routed to separation or containment equipment before final discharge to a flare or scrubber. 

Flare Gas - Molecular weight, lower explosive limit, density at flare tip, fraction F of heat release radiated by the flame. 

Cl = Lower explosive limit concentration of flare gas in air, volume fractions... 

The following discussion provides a plant caculation method for lower explosion limit concentrations for flare stacks or leaking valves that could ignite. 

Flare stack diameter (as calculated before) = 0.496 m Tip exit velocity (as calculated before) = 210 m/sec Lower explosive limit of gas (Equation 4.102, Table 4.17) = 0.0397 mol fraction... 

Roussakis, N. 1988. The Hazard of an Oil Storage Tank Explosion from Lightning Strike at a Flare Stack. Technical Paper (May 1988). Westech Industrial Limited, Calgary, Alberta, Canada... 

U = lateral wind velocity, ft/sec Uj = flare tip velocity, ft/sec UEL = upper explosive or flammable limit, percent of mixture of flammable gases only in air... 

The Hydrocarbon Processing Industry (HPI), has traditionally been reluctant to invest capital where an immediate direct return on the investment to the company is not obvious, as would any business enterprise. Additionally financial fire losses in the petroleum and related industries were relatively small up to about the 1950 s. This was due to the small size of facilities and the relatively low value of oil and gas to the volume of production. Until 1950, a fire or explosion loss of more than 5 million U. S. Dollars had not occurred in the refining industry in the USA. Also in this period, the capital intensive offshore oil exploration and production industry were only just beginning. The use of gas was also limited early in the century. Consequentially its value was also very low. Typically production gas was immediately flared or the well was capped and considered as an uneconomical reservoir. Since gas development was limited, large vapor explosions were relatively rare and catastrophic destruction from petroleum incidents was essentially unheard of. The outlays for petroleum industry safety features were traditionally the absolute minimum required by governmental regulations. The development of loss prevention philosophies and practices were therefore not effectively developed within the industry. 

Uses Shows limited use in military dynamites when mixed with nitroglycerine, fireworks, flares, and explosives compositions when mixed with TATB, or DATB. ... 

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