---
title: "CFB boiler (circulating fluidised bed)"
description: "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."
canonical_url: "https://sylio.co/glossary/cfb-boiler"
last_updated: "2026-06-28T02:29:26.102Z"
---

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](/glossary/cyclone-separator). Combustion temperature (~850 °C) is much lower than in a [PC boiler](/glossary/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](/glossary/waste-to-energy) (wood, agricultural residues, bagasse)
- [RDF](/glossary/rdf-srf-tdf) 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](/glossary/economiser), [superheater](/glossary/superheater) and [air-heater](/glossary/air-heater) tubes
- **Refractory wear** in high-velocity zones

[Sonic horns](/glossary/sonic-horn) on the backpass surfaces and cyclone walls extend run length between maintenance outages.

## Related terms

- [Boiler](/glossary/boiler)
- [BFB boiler](/glossary/bfb-boiler)
- [PC boiler](/glossary/pc-boiler)
- [Cyclone separator](/glossary/cyclone-separator)
- [Sonic horn](/glossary/sonic-horn)