Boilers
Circulating fluidised-bed boiler
Also known as CFB boiler, circulating fluidised bed boiler, circulating fluidized bed.
A circulating fluidised-bed (CFB) boiler burns fuel in a turbulent bed of sand, ash and limestone, circulated by an upward-flowing combustion-air stream and recirculated through external cyclone separators. Combustion temperature (~850 °C) is much lower than in a PC boiler, giving naturally lower NOx and the capability to capture SO₂ in the bed by limestone addition.
Fuel flexibility
CFB boilers tolerate a far wider range of fuels than PC boilers:
- Coal (anthracite, bituminous, sub-bituminous, lignite)
- Petroleum coke
- Biomass (wood, agricultural residues, bagasse)
- RDF and waste fractions
- Mixed and low-grade fuels
This fuel flexibility makes CFB the technology of choice for biomass conversions, waste-fired plants and lignite-rich regions.
Fouling pattern
- Cyclone fouling — recirculating bed material accumulates on cyclone walls and downcomers
- Backpass fouling — fine ash on economiser, superheater and air-heater tubes
- Refractory wear in high-velocity zones
Sonic horns on the backpass surfaces and cyclone walls extend run length between maintenance outages.
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.
- Pulverised-coal boilerA pulverised-coal boiler grinds coal to fine powder and injects it through burners into a furnace. The dominant utility-scale boiler design worldwide.
- Cyclone separatorA cyclone separator removes particulate from a gas stream by centrifugal force. Wall build-up and re-entrainment from the dipleg are the dominant operational issues.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.