In a pulverized coal boiler, what is the role of primary air and secondary air?

• A. Primary air provides cooling; secondary air pressurizes the boiler.
• B. Primary air carries pulverized coal to the furnace; secondary air provides the bulk of combustion air with proper mixing for flame stability and complete combustion.
• C. Primary air is the main combustion air; secondary air is unused.
• D. Primary air removes ash; secondary air heats feedwater.

Answer: (B)

In a pulverized coal boiler, the air stream is split to handle fuel transport and combustion air separately. Primary air acts as the carrier for the pulverized coal from the mill to the furnace, helping to fluidize and entrain the coal so it can be blown into the burner without clogging. Secondary air provides the bulk of the oxygen for combustion and is introduced near the burners to mix with the coal-air jet, ensuring proper flame stability and complete combustion. This arrangement allows efficient fuel delivery while giving good control over the air-fuel mix and flame characteristics. The other statements don’t fit this setup—primary air isn’t primarily for cooling, secondary air isn’t unused, and ash removal or feedwater heating aren’t roles of these air streams.