Boilers
Waterwall
Also known as water wall, membrane wall, furnace wall.
Waterwalls are panels of vertical evaporator tubes welded into a gas-tight membrane that line the furnace walls of an industrial boiler. They absorb the radiant heat of the burning fuel and produce most of the boiler's steam.
Construction
Adjacent tubes are connected by a thin steel fin running their full length, forming a continuous gas-tight pressure boundary. Tube diameters are typically 38–63 mm, on 50–80 mm pitches. Wall sections can be hung from headers above (suspension waterwalls) or supported from below (sit-on).
Fouling: slag, not ash
Furnace temperatures and radiant heat transfer mean that any ash that hits the waterwall is partly molten. Cooled rapidly against the tube wall, it solidifies as slag. Slag is hard, bonded, and grows in characteristic patterns: thicker near burner clusters, thinner in cold corners.
Cleaning waterwalls
Sonic horns are not effective on hard furnace slag — the deposit is too well-bonded for acoustic energy to dislodge. The standard cleaning tools are:
- Water cannons — high-pressure water lances mounted on the waterwall, fired at specific tube sections
- Wall blowers — short retract sootblowers with multiple nozzles
- Explosive deslagging — periodic shock cleaning for severe build-up
Tube failures on waterwalls
Tube erosion and tube wastage on waterwalls are the leading cause of forced outages on coal-fired and biomass boilers. Mitigation is largely combustion-control rather than cleaning, but excessive aggressive cleaning (especially water cannons) contributes to thermal-fatigue cracking.
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.
- Furnace (boiler)The furnace is the radiant chamber of a boiler where fuel burns at 1,300–1,700 °C. Waterwalls absorb the radiant heat; molten slag is the dominant fouling concern.
- SlaggingSlagging is the deposition of molten or semi-molten ash on radiant and high-temperature surfaces in the boiler furnace. Hard, bonded; usually requires water cannons or explosive deslagging.
- Tube erosion and tube wastageTube erosion is the gradual thinning of boiler tubes by fly-ash impact and sootblower steam jets. Both are documented mechanisms of boiler tube failure.
- Water cannonA water cannon projects a high-pressure water jet onto boiler waterwalls to crack slag deposits by thermal shock. The standard cleaning tool for furnace slag, with care for tube fatigue.