Two main types of deposits in boilers.
Slagging
- Deposits
within furnace, in areas directly exposed to flame radiation such
as furnace walls and some widely spaced pendant super-heaters.
- Take
place in the hottest parts of boiler
Fouling
- Deposits
in areas NOT directly exposed to flame radiation such as the more
closely spaced tubes in convection sections of boiler
- Take
place as flue gas & suspended fly ash cool down
Effects of
deposition on boiler performance
-
Reduction of heat transfer from combustion gas to water-steam
- Lead to
an increase in gas temperature
- Lead to
a further increase in deposition rate
- Result
in continually changing conditions in boiler.
The formation mechanisms of slagging and fouling
is very different for both forms of boiler deposits. While indices
calculated based on bulk ash properties can be useful for the
estimation of a coal propensity to slag or foul, these indices very
rarely simulated the mechanisms involved. For an accurate
estimation of where and the extend of slagging and fouling requires
knowledge of the distribution and size of the minerals species in a
coal particle and free minerals coupled with detailed knowledge of
the gas flows from the burners through the boiler.
