How an Incinerator Works

If you're a city person, once a week you probably take your household trash down to the curb. Apartment dwellers probably take their trash to a dumpster a few times a week. The rest of you know what you do with yours. All this trash must be disposed of somewhere, often a landfill, but sometimes an incinerator. Both disposal options are controversial, but often the incinerator is more so even though people burned trash and garbage long before trashcans and dumpsters were invented. .

In addition to municipal waste incinerators, there are incinerators that burn sludge, a mixture of solids removed from various wastewater treatment processes; incinerators that burn industrial waste; and cement kiln incinerators that burn chemical wastes.

Incineration is beneficial because it reduces the volume of waste that goes into a landfill, destroys pathogens in medical waste, destroys some toxics and hazardous materials, and produces steam or electricity if the incinerator is a waste-to-energy facility. Those who oppose incinerators do so for various reasons including the fact that residues from burning contain toxic chemicals, such as dioxins and furans; and metals, such as cadmium, lead and arsenic.

There are three kinds of waste-to-energy incinerators: mass burn, modular and refuse-to-fuel (RDF - refuse-derived fuel).

Mass burn and modular incinerators use unsorted trash. Refuse-derived fuel facilities shred the waste and then sort the recyclables (glass, metal) and unburnables (stone, grit) from the nonrecyclables with screens and magnets, and shred again to make a uniform size fuel so the final fuel burns better and produces more energy.

Modular incinerators work like mass burn incinerators but are smaller, often prefabricated, and easier to put in place. Refuse-to-fuel incinerators cost more to build and run, and most are generally unprofitable so many have been converted to mass burn.

At all the facilities, trash may be stored temporarily until it is either transferred to a feed unit (mass burn and modular) or sorted (RDF) and then sent to a feed unit. Waste is then either lifted by crane into the furnace or kiln, or fed to the furnace by a hopper. The hopper feed process isn't much different from today's home wood pellet stoves. For a pellet stove, an owner places wood pellets into a feed unit or hopper, which feeds the pellets into the fireplace.

Trash burns in a furnace at more than 1500 degrees. The greatest amount of residue from burning is bottom ash and materials that don't burn. These drop to the bottom of the furnace and are collected for disposal in either an ash landfill or a municipal landfill. Similarly, at home, an owner must remove the ashes from a fireplace, wood burning stove or pellet stove and dispose of the ashes either in their trash or around bushes and plants in their backyards and gardens.

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