Glossary
Boilers
Hog-fuel boiler and bark boiler
Also known as hog fuel boiler, bark boiler, power boiler (pulp mill).
A hog-fuel boiler (or bark boiler, sometimes generically power boiler) is a biomass-fired auxiliary boiler installed at most pulp and paper mills to burn wood waste, bark, sawdust and screened biomass residues, supplying additional steam and electricity alongside the kraft recovery boiler.
Combustion types
| Type | Fuel handling |
|---|---|
| Grate-fired | Older designs, simple, tolerates wet fuel |
| BFB | Common modern design for variable biomass |
| CFB | Larger capacity, broader fuel flexibility |
Fouling characteristics
- Alkali- and chloride-rich ash from bark and forest residues
- High variability in fuel moisture and composition
- Slagging on first-pass tubes; bonded ash on superheaters
- Cold-end build-up on the economiser and air heater
Sonic-horn fit
Sonic horns are well established on hog-fuel-boiler convective passes; the OEM aftermarket teams that serve recovery boilers also typically include hog-fuel cleaning in the same service contract.
Related terms
Related terms
- BoilerA boiler is a vessel that converts fuel chemical energy into steam by heating water. Coal-fired, biomass, oil, gas and recovery boilers all foul; sonic horns clean heat-transfer surfaces.
- Bubbling fluidised-bed boilerA BFB boiler suspends fuel in a slowly-bubbling bed of inert solids. Lower fluidisation velocity than CFB; suited to high-moisture biomass and sludges.
- Circulating fluidised-bed boilerA CFB boiler burns fuel in a turbulent bed of sand, ash and limestone circulated by an upward-flowing gas stream. Tolerates coal, biomass, RDF and lignite; produces low NOx.
- Recovery boilerA recovery boiler burns kraft black liquor to generate steam, electrical power and recovered pulping chemicals. Iconic application for sonic horns on superheater cleaning.
- SuperheaterA superheater is a tube bank that raises steam temperature beyond the saturation point using flue-gas heat. Sticky alkali ash and slag deposits are the dominant fouling concerns.