Acid dew point (ADT) of sulfur-bearing flue gas—typical value For a fuel containing about 1% sulfur, the acid dew point temperature of the flue gas is typically closest to which value (°C)?

Introduction / Context:
Acid dew point (ADT) is the temperature at which acid vapors (mainly H2SO4 formed from SO3 and water vapor) condense from flue gases. Below ADT, severe low-temperature corrosion of carbon steel surfaces can occur. Estimating ADT guides minimum safe metal and gas temperatures at economizers, air preheaters, and stacks.

Given Data / Assumptions:

• Sulfur content in fuel ≈ 1% by mass.
• Typical excess air and flue-gas moisture content for industrial furnaces/boilers.
• Usual SO2 to SO3 conversion levels in conventional firing.

Concept / Approach:
H2SO4 condensation temperature depends on partial pressure of SO3 and H2O. For common industrial conditions with around 1% sulfur and modest SO3 formation, ADT often lies near 120–140°C. Operators therefore avoid allowing cold-end surfaces to fall below this range to prevent acid corrosion and fouling.

Step-by-Step Solution:

Verification / Alternative check:
Field guidelines for air preheater cold-end metal temperatures commonly target > 120–130°C at 1% S fuels to avoid acid dewpoint corrosion.

Why Other Options Are Wrong:

• 80°C: too low; would risk heavy acid condensation well before this temperature.
• 180°C or 250°C: associated with unusually high SO3 partial pressures or atypical conditions.

Common Pitfalls:
Confusing water dew point with acid dew point; the latter is significantly higher in sulfur-bearing flue gases.

Final Answer:
130