Boilers
Economiser
Also known as economizer, feedwater economiser.
An economiser is the tube bank in a boiler's convective pass that recovers residual heat from the flue gas by preheating boiler feedwater. It sits downstream of the reheater and upstream of the air heater; economiser performance directly affects boiler heat rate.
Fouling
Two failure modes dominate:
- Ash bridging between tubes — gas can no longer pass freely; ΔP across the economiser rises
- Large-particle ash dropping out of the gas stream onto economiser hoppers — bridges and pluggage in the hopper itself
The first reduces gas-side heat transfer and forces gas channelling around the blocked area; the second causes hopper extraction to fail and back-pressures the gas path.
Sonic-horn duty
Sonic horns mounted on the economiser shell and hopper are particularly effective because economiser deposits are dry, friable and respond well to acoustic dislodging. Plants commonly report 1–2% boiler-efficiency recovery after horn installation on heavily-fouled economisers.
Economiser-SCR adjacency
On units with an upstream high-dust SCR, the economiser receives the same large-particle ash that the SCR is designed against. LPA screens between SCR and economiser are common; sonic horns help keep both surfaces clean.
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.
- Convective pass and backpassThe convective pass is the downstream section of a boiler where heat transfer is by conduction across tube banks: superheater, reheater, economiser. The primary zone for sonic-horn 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.
- Air heaterAn air heater (also air preheater, APH) recovers low-grade heat from flue gas to preheat combustion air. Cold-end fouling and corrosion are the dominant operational challenges.
- Large-particle ashLPA is fly ash larger than typical (>1 mm), produced by slag fragmentation and agglomeration in the boiler. It is the leading cause of SCR catalyst channel pluggage.
- 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.