Pulverized versus lump coal firing: Compared with burning lump coal, which statement about combustion of pulverized coal in furnaces is correct?

Introduction:Pulverized coal firing is widely used in utility boilers because finely ground particles present a very high surface area for rapid devolatilization and combustion. Recognizing how this affects flame characteristics, air requirements, and heat release helps in selecting firing systems and tuning combustion for efficiency and emissions.

Given Data / Assumptions:

• Pulverized coal particles (typically < 75 μm) vs. large “lump” coal.
• Well-designed burners with good air–fuel mixing.
• Goal: complete combustion with minimal excess air.

Concept / Approach:Fine particles ignite quickly, releasing volatiles and burning more completely over short residence times. Better mixing and rapid kinetics reduce the need for high excess air. Flames are generally hot and often luminous due to incandescent carbon particles. The overall heat release rate per furnace volume is higher, enabling compact boilers with high steaming capacity.

Step-by-Step Solution:High surface area → faster reactions → lower required excess air for complete burnout.Rapid combustion → higher flame temperatures (not “low”).Incandescent particles → luminous flame (not “non-luminous”).Intense burning → higher, not lower, volumetric heat-release rate.

Verification / Alternative check:Boiler tuning practice shows reduced O2 setpoints and improved efficiency with proper pulverized-fuel milling, classification, and burner staging.

Why Other Options Are Wrong:

• Non-luminous/low-temperature: Opposite of typical pulverized-coal flames.
• Lower heat release: False; pulverization increases heat release per volume.
• Reduced efficiency: Properly fired pulverized-coal boilers achieve high efficiencies.

Common Pitfalls:Confusing pulverized-coal flames with gaseous, non-sooty premixed flames, which tend to be less luminous.

Final Answer:can be done with less excess air