16/12/2025
1 Secondary combustion in superheater zones
The furnace begins to starve when the air ingress is more from roof seal box / Convection SH seal box.
The leakage air allows secondary combustion of volatiles. The SH temperature becomes
uncontrollable. Particularly at the time of load variation, the fuel feeder rpm is regulated by the
operator and he finds the SH steam temperature rises faster than the pressure. This is seen in boilers
fired with biomass fuels.
2 Secondary combustion in Boiler bank hoppers
The Unburnt fuels burn at the boiler bank ash hoppers, since the furnace is at substochiometeric
conditions when there is air ingress is present downstream. The unburnt fuel travels downstream
instead of completely burning in the furnace. The ash hoppers get distorted due to secondary
combustion.
3. Ash blockages in boiler bank Baffles
When the ash is not fully burnt in the furnace, the flow ability of ash comes down. The ash particles
now contain fuel particles which may be fibrous / irregular in nature. Thus the fuel and ash settle at
every possible location, where the surfaces are less inclined or flat. The ash does not flow freely and
thus ash accumulates at baffles. Whatever the draft is set the ash does not flow due to nature of the
accumulations.
4. Ash blockages in Hoppers
Carryover of fuel particles to ash hoppers would lead to combustion in ash hoppers. Lumps form due
to static combustion. We try to poke the ash drain pipes but situations repeat often. The combustion is
not complete at the furnace and hence the troubles.
