Waste-to-energy and biomass
Air-pollution-control residue
Also known as APC residue, APCr, WtE fly ash, air pollution control residue.
APC residue (air-pollution-control residue, or APCr) is the fine fly-ash combined with reagent salts (calcium hydroxide, activated carbon, sodium bicarbonate) captured by the flue-gas-treatment train downstream of a WtE boiler. APC residue typically accounts for 2–5% of original waste mass — much less than incinerator bottom ash (IBA), but more hazardous because heavy metals (Hg, Pb, Cd) and dioxins concentrate here.
Classification and disposal
In the EU and UK, APC residue is classified as hazardous waste. Disposal routes include:
- Stabilisation and landfilling in specialised hazardous-waste facilities
- Underground storage (former salt mines in Germany)
- Treatment for partial reuse in construction materials
- Specialised commercial processing for metals recovery
Sonic-horn relevance
APC residue is collected in fly-ash hoppers below the boiler economiser, SCR, baghouse and any reagent-injection equipment. Hopper bridging is a frequent problem because APC residue is fine, sticky and partly hygroscopic. Sonic horns on APC-residue hoppers are routine specification on modern WtE plants.
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.
- Incinerator bottom ashIBA is the non-combustible residue discharged from the bottom of a WtE grate-fired boiler. Mostly inert; can be processed for aggregate reuse or landfilled.
- BaghouseA baghouse is the structural enclosure that holds the bags, cages, tubesheet, cleaning system and hoppers of a fabric-filter dust collector. Sized in compartments for online isolation.
- Fly-ash hopperA fly-ash hopper collects particulate ash from ESP, baghouse, economiser and air-heater equipment. Bridging and rat-holing of fly ash are persistent operational problems.