Flare Stack Sizing Calculator
Calculate minimum flare stack height, tip diameter, and thermal radiation contours per API 521 methodology.
Flare Parameters
Results
Min Stack Height
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Tip Diameter
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Total Heat Release
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Radiated Heat
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Radiation Intensity at Key Distances
| Distance from Base (ft) | Radiation (BTU/hr/ft²) | Personnel Exposure |
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Radiation vs Distance from Flare Base
How this was calculated
Heat release: Q_total = W * Hc (BTU/hr). Radiated heat: Q_rad = Q_total * F.
Stack height (API 521): H = sqrt(Q_rad / (4 * pi * K_max)), where K_max is the allowable radiation at grade level.
Tip diameter: Sized for Mach 0.2 exit velocity. D_tip = sqrt(4*W / (pi * rho * V_sonic * 0.2 * 3600)), with gas density at relief conditions.
Radiation at distance: K(r) = Q_rad / (4 * pi * r^2), where r = sqrt(d^2 + H^2) is the distance from the flame center to the receptor.
Exposure limits: 500 BTU/hr/ft2 (equipment, 8hrs), 1500 BTU/hr/ft2 (personnel w/ protection, brief), 2000 BTU/hr/ft2 (emergency, seconds).
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Book a free strategy call →Flare Stack Sizing and API 521
Flare stack sizing is a critical safety calculation in oil and gas facility design. The primary objective is to ensure that thermal radiation levels at grade and at occupied areas do not exceed safe limits during emergency relief events. API Standard 521 (Pressure-relieving and Depressuring Systems) provides the methodology for determining flare stack height and tip diameter.
The stack height is governed by the allowable radiation at grade level. For areas where personnel may be present for extended periods, radiation limits of 500 BTU/hr/ft2 are typically applied. Higher limits (1,500-2,000 BTU/hr/ft2) may be acceptable for brief emergency exposure with protective clothing.
Tip diameter is sized to maintain a Mach number of approximately 0.2 at the tip exit. Higher Mach numbers can cause flame instability, noise, and potential flame lift-off. Lower velocities waste material and increase tip cost. Wind speed affects flame tilt and can significantly alter the radiation pattern at grade.
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