Coal loss in carryover ash from boilers The fraction of combustibles escaping with fly ash depends on which group of operating and fuel variables?

Introduction / Context:
In pulverised-coal and other solid-fuel boilers, unburnt carbon can escape with fly ash, reducing efficiency and increasing particulate emissions. Understanding what drives this loss helps optimize combustion and cut fuel waste.

Given Data / Assumptions:

• Carryover loss refers to unburnt carbon in ash leaving the boiler.
• We consider fuel properties, air/firing conditions, and equipment design.

Concept / Approach:
Unburnt loss rises when particles are too large (short residence time to burn), when mixing/air distribution is poor, or when burners and chamber geometry do not promote complete burnout. Operating load and excess air affect residence time, temperature, and oxygen availability. Fuel properties (ash content, grind fineness, volatiles) and burner design strongly influence flame stability and burnout.

Step-by-Step Solution:

Verification / Alternative check:
Heat balance tests correlate loss on ignition (LOI) in fly ash with grind fineness, burner settings, and load—matching the multi-factor dependence.

Why Other Options Are Wrong:

Common Pitfalls:
Over-grinding raises mill power with diminishing returns; better air distribution and burner tuning often give larger reductions in unburnt carbon.

Final Answer:
all (a), (b) and (c)