Waste to energy: incineration grown up

Waste to energy occupies an odd position: environmentally it outranks the landfill it replaces and underranks the recycling it must not displace; commercially it is a thirty-year infrastructure asset fed by a supply chain of bin lorries. The technology is mature. The projects that fail, fail on fuel arithmetic and residue planning, not combustion.

The reference plant

The world's dominant design is the moving-grate mass-burn unit: waste combusts on a reciprocating grate at 850–1,100 °C, raises steam at typically 40–60 bar and 400 °C — conservative figures forced by chloride corrosion, not ambition — and a condensing turbine converts perhaps a quarter of the fuel energy to electricity. Add district heating or process steam offtake and total efficiency climbs past 60 per cent; the R1 formula that classifies a plant as recovery rather than disposal rewards exactly this. Fluidised beds take shredded, homogeneous fuels; gasification and pyrolysis remain the sector's perpetual next decade, with a track record that advises caution.

Output	Share	Destination
Electricity	500–650 kWh	Grid, less parasitic load
Heat (where offtake exists)	up to 2 MWh	District heating / industry
Bottom ash	20–25 % by mass	Metals recovery, then aggregate
APC residues	3–5 % by mass	Hazardous — stabilisation and disposal

Flue gas and residues — the real environmental engineering

Modern flue-gas treatment — SNCR or SCR for NOx, lime or bicarbonate scrubbing for acid gases, activated carbon for mercury and dioxins, bag filtration for the lot — holds emissions to fractions of the limits that made incineration's old reputation. The residues inherit the problem: bottom ash is a manageable product with a metals dividend, while air-pollution-control residues are hazardous waste requiring stabilisation. A project without a permitted APC residue route is not a project.

Where the projects go wrong

• Feedstock guarantees: put-or-pay tonnages signed against optimistic waste-growth forecasts, colliding with recycling targets that shrink the same tonnes.
• Calorific drift: as organics are diverted to digestion, heating value rises and mass throughput falls — plants hit thermal limits below nameplate tonnage.
• Heat offtake assumed, never contracted — the efficiency case quietly halves.
• Gulf specifics: high-moisture, high-inert waste streams and summer condenser temperatures both cut output; designs transplanted from Europe without re-rating disappoint.

Done properly — sized against conservative waste forecasts, with contracted heat users and residue routes secured before financial close — EfW is sober, useful infrastructure that turns a disposal liability into baseload energy. Done as a gate-fee speculation, it is a claims file with a chimney.