Input Parameters

Enter relief gas properties and conditions

Flare Type

Relief Rate (lb/hr)

Molecular Weight

Methane=16, Propane=44

Relief Temperature (F)

Relief Pressure (psig)

Heat of Combustion (BTU/lb)

NG~21500, Propane~21600

Radiation Fraction

Typical: 0.15-0.30

Wind Speed (mph)

Stack Height (ft)

Or calculate below

Tip Exit Velocity (ft/s)

Flare Sizing Results

Flare Tip Diameter

Tip Sizing

Required Tip Diameter -

Standard Tip Size -

Exit Velocity -

Mach Number -

Flame Characteristics

Flame Length -

Flame Tilt Angle -

Heat Release Rate -

Thermal Radiation Distances

500 BTU/hr-ft2 (8 hr work) -

1500 BTU/hr-ft2 (escape) -

2000 BTU/hr-ft2 (brief) -

3000 BTU/hr-ft2 (equipment) -

Stack Requirements

Min Stack Height (grade level) -

Exclusion Zone Radius -

Enter parameters and click Calculate

API 521 Radiation Limits

500 BTU/hr-ft2: 8-hour continuous exposure
1500 BTU/hr-ft2: Escape routes (clothing ignition)
2000 BTU/hr-ft2: Brief exposure (evacuation)
3000 BTU/hr-ft2: Equipment/structures

Formula Reference

Flare Tip Diameter (API 521)

Tip Diameter: d = sqrt((4 * W) / (pi * rho * V)) Where: d = Tip diameter (ft) W = Relief rate (lb/s) rho = Gas density at tip (lb/ft3) V = Exit velocity (ft/s) Gas Density at Tip: rho = (P * MW) / (10.73 * T * Z) Sonic Velocity: Vs = sqrt(k * R * T / MW) = 223 * sqrt(k * T / MW) ft/s

Flame Length (Brzustowski)

Flame Length: L = 0.00326 * Q^0.478 Where: L = Flame length (ft) Q = Heat release rate (BTU/hr) Heat Release Rate: Q = W * Hc Where: W = Mass flow rate (lb/hr) Hc = Heat of combustion (BTU/lb)

Thermal Radiation (API 521)

Radiation Intensity: I = (F * Q) / (4 * pi * D^2) * tau Where: I = Radiation intensity (BTU/hr-ft2) F = Fraction of heat radiated (0.15-0.30) Q = Heat release (BTU/hr) D = Distance from flame center (ft) tau = Atmospheric transmissivity (~1.0) Distance for Given Intensity: D = sqrt((F * Q) / (4 * pi * I))

Flare System Sizing Calculator