Waste-to-energy and biomass
Chloride-induced corrosion
Also known as Cl corrosion, chloride corrosion, high-temperature chloride corrosion.
Chloride-induced corrosion is the accelerated tube-wall thinning caused by chlorine-rich deposits on the steam-side surfaces of WtE, biomass and waste-fired boilers. Chloride corrosion is the dominant tube-failure mechanism in WtE and a major maintenance cost driver.
Mechanism
Chlorine in the fuel enters the gas phase as HCl and metal chlorides. Inside a thin deposit on the tube, chloride and metal-chloride species shuttle electrons between the gas atmosphere and the tube surface. The result is rapid metal loss far in excess of what the temperature alone would predict. The "active oxidation" mechanism describes one variant; chloride attack on the protective oxide scale describes another.
Where it dominates
- WtE superheaters — design temperatures kept low (380–420 °C) specifically to limit chloride corrosion
- Straw-fired boilers — see straw firing
- RDF / SRF boilers — variable but generally high
- Heavy-petroleum-fired boilers with chloride contamination
Mitigation
- Material selection — Inconel-625 weld overlays, nickel-based alloys on the most-exposed tubes
- Lower steam temperature at the superheater outlet to keep tube-metal below the corrosion threshold
- Fuel control — limit chloride loading where the contract permits
- Sonic horns — preventing deposits from consolidating reduces the chloride concentration immediately adjacent to the tube surface, indirectly slowing corrosion
Related terms
Related terms
- Waste-to-energyWtE plants burn municipal solid waste, RDF, SRF and biomass to generate steam and electricity. Sticky chloride-rich ash defeats conventional cleaning; sonic horns are the dominant fit.
- Alkali metals in ashAlkali metals (Na, K) in biomass and waste-fuel ash form low-melting compounds that bond to boiler tubes as sticky deposits and poison SCR catalysts.
- Low-melt sticky ashLow-melt sticky ash forms when alkali-rich ash particles soften at typical convective-pass temperatures and bond to tube surfaces. Defeats steam sootblowers; primary target for sonic horns.
- Cold-end corrosion and dew-point corrosionCold-end corrosion is the attack on air-heater and economiser surfaces below the acid dew point, where SO3 condenses as sulphuric acid. The leading cold-end failure mechanism.
- 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.