HomeFlare SystemsStack height calculator
    Flare Systems

    Engineering tool

    Flare Stack Height

    Preliminary estimate of the stack height required to keep thermal radiation at a receptor below an allowable level, following the method of API 521 Annex C. Every intermediate quantity is shown: the point of this tool is that you can check it, not that you have to trust it.

    Release
    Gas properties
    Geometry & wind
    Radiation criterion
    Flame length correlation

    Two different coefficient sets are in circulation for L = c·Q^e and they differ by around 40% on the same release. Use the values from the edition of API 521 you work to.

    Estimated stack height

    38.8 m

    U∞ 8.0 m/sL = 88.3 mθ 11.4°flame centreD = 96.8 mK = 1.58 kW/m²stack 38.8 m60.0 m
    Drawn to scale from the values entered. The two distances are not the same thing: the one along the ground is where the receptor is, D is the slant distance from the centre of the flame — and it is D that carries the radiation. The height is what has to grow until D is large enough.
    Intermediate resultValueRelation
    Heat release930.0 MWQ = qm · LHV
    Flame length88.3 mL = c · Q^e
    Volumetric flow at tip11.19 m³/sqv = (qm/MW) · Z · R · T / p
    Exit velocity39.6 m/sUj = qv / A
    Mach number at tip0.152 –Ma = Uj / c₍gas₎, γ = 1.2
    Flame tilt from vertical11.4 °θ = atan(U∞ / Uj)
    Flame centre offset8.7 / 43.3 m (x / y)Δx = L/2·sinθ, Δy = L/2·cosθ
    Required flame-to-receptor distance96.8 mD = √(τ·F·Q / 4πK)

    Preliminary estimate

    This is a screening calculation, not a verification. It uses a simplified flame tilt model, assumes a single receptor and a single wind condition, and does not check dispersion of an unignited release — which frequently governs the height instead. It is not a substitute for a flare study and carries no warranty.

    Need the real calculation?

    Send us the relief load summary and the plot plan and we will tell you what governs the height — radiation, dispersion or layout.

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