Heat Duty + Firetube + Coalescing Section per API 12L
Emulsion breaking with heat + chemical, firetube heat flux limits, coalescing section design, vertical vs horizontal selection.
Heat duty (sensible):
W (lb/hr) = BPD × SG × 350.5 / 24
Total duty with losses:
Firetube area:
Burner & fuel gas:
Coalescing section (horizontal):
Vertical diameter (downflow vs settling):
Beggs-Robinson dead-oil viscosity at T:
Heater treater sizing has four parts: (1) heat duty Q = W·Cp·ΔT, (2) firetube area A = Q/q″ at 10,000 Btu/hr·ft² (API 12L max 15,000), (3) burner sized for 1.25× turndown plus fuel-gas rate, and (4) coalescing section sized for small-droplet (100–250 µm) water settling.
By API band: > 35° → 120°F; 25–35° → 150°F; 15–25° → 180°F; < 15° → 220–300°F. Higher T breaks tougher emulsions but burns more fuel and may push downstream RVP off spec.
FWKO = cold gravity drop of free water only. Heater treater = heat + chemical (and sometimes electrostatic) to break emulsified water. High water cut typically wants both: FWKO upstream to take 90% of free water cheaply, then treater finishes oil to ≤ 1% BS&W.
API 12L caps the firetube wetted-wall flux at 15,000 Btu/hr·ft². Most designs use 10,000 Btu/hr·ft² to avoid coking and extend firetube life. Above 12,000 the coking risk rises sharply in sour or paraffinic crudes.