Large-scale waste-to-energy: Working principle

Large-scale waste-to-energy: Working principle.

 

Waste is fed into a closed receiving area and thoroughly mixed in preparation for combustion.

 

The mixed waste enters the combustion chamber through a timed-moving grate, which repeatedly turns the waste to ensure complete combustion.

 

Fine airborne particles (fly ash) are removed in a baghouse dust collector. Acidic combustion gases are neutralized by injecting lime or sodium hydroxide.

 

The unburned residue—"bottom ash"—passes through a magnetic and eddy current separator to remove ferrous metals (steel and iron) and other metals such as copper, brass, nickel, and aluminum for recycling. The remaining ash can be used as aggregate for roadbeds and railway embankments.

 

Superheated steam drives a steam turbine generator. The cooled steam is circulated back to water via a condenser or used as a heat source for buildings or industries. The cooled steam is reheated in an economizer and superheater, completing the steam cycle.

 

Activated carbon (charcoal treated with oxygen to increase its porosity) is injected into high-temperature flue gas to absorb and remove heavy metals such as mercury and cadmium. Nitrogen oxides in the rising combustion gases are neutralized by injecting ammonia or urea. Dioxins and furans are destroyed by exposure to extremely high temperatures in the flue gas.