Boiler Acid Dew Point & Cold End Corrosion Calculator
Determine sulfuric acid vapor condensation temperature ($T_{adp}$), flue gas $SO_3$ concentration, and air preheater minimum metal temperature margin.
Fuel Chemistry & Flue Gas
Acid Dew Point & Corrosion Prevention
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Verhoff-Banchero Acid Dew Point Chemistry
During fossil fuel combustion, sulfur burns to sulfur dioxide ($SO_2$). In the high-temperature furnace and across vanadium/iron catalyst deposits, a small fraction ($1\%$ to $4\%$) oxidizes into sulfur trioxide ($SO_3$). Below $300^\circ\text{C}$, $SO_3$ instantly hydrates with flue gas moisture to form sulfuric acid vapor ($H_2SO_4$).
Cold-End Air Preheater Corrosion
Even a tiny concentration of $SO_3$ (just $15\text{ to } 30\text{ ppm}$) raises the dew point of the flue gas from $50^\circ\text{C}$ (pure water dew point) up to $135^\circ\text{C} - 150^\circ\text{C}$ ($275^\circ\text{F} - 300^\circ\text{F}$). If rotary air heater baskets, baghouse filters, or ID fan casings drop below this temperature, concentrated ($70 - 85\%$) sulfuric acid condenses, corroding carbon steel plates within weeks.