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)?
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A80
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B130
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C180
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D250
Answer
Correct Answer: 130
Explanation
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:
Relate sulfur in fuel to SO2 and small SO3 formation.Recognize that higher SO3 or moisture increases ADT; lower values reduce it.Choose the representative value around the middle of common practice: ~130°C.Reject far lower (80°C) or much higher (180–250°C) values for the stated sulfur level.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