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Multi-Source Flare Load (API 521)

Safety & relief · Flare header & tip Mach · API 521 §5/§7

Multi-Source Flare Load & Header
Groups relief sources by contingency, picks the governing case, and computes flow-weighted mixture properties, flare-tip Mach (API 521 limit), header Mach and built-up back-pressure. Enter rate + MW for each source; tag a contingency to group simultaneous loads.

Relief Sources (rate + MW required)

kg/hMW°CContingency

Geometry & Properties

in
in
m

Engineering Basis

  • Relief LOAD governed by the largest summed simultaneous mass rate; tip-Mach, header-Mach and back-pressure are evaluated for EVERY contingency and the worst reported (a lighter/hotter low-mass case can choke the tip).
  • Mixture MW = W/Σ(Wi/MWi); mass-weighted temperature.
  • Tip: ρ = P·MW/RT (atmospheric exit), Mach = v/√(kRT/MW); API 521 §5 limit ≤0.5 emergency / ≤0.2 continuous.
  • Header Mach at tip density; ΔP Darcy (incompressible, conservative) → built-up back-pressure.
  • Standards: API 521 7th Ed §5/§7, GPSA EDB 14th Ed §5.