Calculators
Fired Heater Stack Design
Natural-draft stack sizing (diameter and height) for a fired heater per API 560 / Wimpress methodology. Calculates flue-gas mass rate, stack gas velocity, available draft per foot of height, and required stack height to overcome system losses.
Method: Stoichiometric air for typical refinery fuel gas ≈ 750 lb air/MMBtu. Flue gas mass ≈ fuel mass + (1+excess) · stoich air. Draft per foot (in H2O/ft) = 0.2554 · Pb · (1/Ta − 1/Ts), T in °R. Required height = (SF · Σlosses) / [draft-per-ft · (1 − f·L/D)], with f ≈ 0.02 steel. Recommended stack velocity 20–40 ft/s. References: API Std 560; API Std 535; Wimpress “Generalized method predicts fired-heater performance”, Chem Eng 1963.
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