Glossary
Fouling
Slagging
Also known as slag deposit, slag bonding, molten slag deposit.
Slagging is the deposition of molten or semi-molten ash on high-temperature surfaces inside a boiler — primarily the furnace waterwalls and the finishing superheater. Slag is distinguished from fouling generally by being formed at temperatures high enough to melt the ash; once cooled against the tube it solidifies as a hard, bonded layer.
Why slag is hard to clean
- Bonded directly to the tube — not a loose surface deposit
- Hardness comparable to the tube metal itself
- Resists acoustic cleaning — sound energy cannot dislodge a bonded interface
- Removable only with high-energy mechanical methods
Cleaning options
| Tool | Use case |
|---|---|
| Water cannon | Standard for furnace waterwall slag |
| Steam retract sootblower | Finishing superheater slag, with care for tube erosion |
| Explosive deslagging | Severe build-up, periodic intervention |
| Manual lancing (offline) | During major outages |
Sonic horns are not effective on furnace slag, but they are effective immediately downstream where deposits cool to a friable consistency. Sylio's value on slag-prone units lies in the convective pass, not in the furnace itself.
Related terms
Related terms
- WaterwallWaterwalls are panels of vertical evaporator tubes welded into a gas-tight membrane that line the furnace. They absorb radiant heat and produce most of the boiler's steam.
- 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.
- 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.
- Fouling (general)Fouling is the accumulation of unwanted deposits on process-equipment surfaces. The general umbrella term covering slagging, scaling, coking, sintering and many other specific mechanisms.
- 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.