Flue-gas conditioning — which additive does NOT reduce acid dew point? In furnace flue-gas treatment, which of the following is not used to reduce the acid dew point of the gas stream?

Introduction / Context:
The acid dew point of flue gas is largely governed by sulfur oxides and water vapor that can condense as acidic mists (e.g., sulfuric acid). Engineers sometimes condition flue gas with alkaline particulates to neutralize acid species and raise the effective dew point margin. Knowing which additives truly help is important for corrosion control and heat recovery.

Given Data / Assumptions:

• Additives considered: dolomite, general alkaline powders, and ammonia.
• Goal: reduce acid dew point to mitigate cold-end corrosion and enable deeper heat recovery.
• Typical acid species: SO3/H2SO4 mist formation.

Concept / Approach:
Alkaline powders such as lime, MgO, or dolomite neutralize acidic species in the gas or on surfaces, thereby reducing the partial pressure of acid vapors and lowering the effective acid dew point at the heat-transfer surfaces. Ammonia, by contrast, can react with SO3 and H2SO4 to form ammonium salts (e.g., ammonium bisulfate) that may increase fouling and do not reduce the acid dew point of the gas; in some cases, they complicate cold-end operation.

Step-by-Step Solution:
Identify additives with basicity: dolomite and alkaline powders neutralize acids.Assess ammonia: forms sticky ammonium salts with SO3/H2SO4, often problematic.Therefore, ammonia is not a dew-point–reducing additive for flue gas conditioning.

Verification / Alternative check:
Cold-end corrosion mitigation guides recommend MgO/lime injection; ammonia is more associated with SCR/SNCR NOx control and can lead to ammonium salt deposition when SO3 is present.

Why Other Options Are Wrong:

• Fine dolomite: A recognized alkaline sorbent for SO3/H2SO4.
• Alkaline powders: Neutralize acidic species and reduce corrosion risk.
• None of these: Incorrect because some listed materials do reduce dew point.

Common Pitfalls:

• Confusing NOx ammonia slip management with acid dew-point control.
• Assuming any reagent that reacts with acid gas is beneficial to dew point; byproducts matter.

Final Answer:
Ammonia