Incineration: merits and demerits

Incineration is the controlled burning of solid waste at high temperature (800-1000 °C or more) in a furnace called an incinerator, which converts combustible waste into ash, flue gas and heat. It is used for waste that is combustible and has a high calorific value (hospital, pathological and hazardous waste), and in cities with little land.

Process

1. Waste is received in a storage pit and fed to the furnace by crane or conveyor.
2. The waste dries and ignites on the grate, then burns with excess air at 800-1000 °C; the flue gases are held at high temperature for about 1-2 s to destroy odours and toxic compounds.
3. The flue gas passes through a heat recovery boiler (for steam or electricity) and then a scrubber, filter or electrostatic precipitator before the chimney.
4. The residual ash and clinker (10-15% of the original volume, 25-30% by mass) are removed and landfilled or used in blocks.

 waste -> [pit] -> [furnace 800-1000C] -> [boiler]
                       |                     |
                     ash/clinker     [scrubber/filter] -> chimney

Merits

• Volume is reduced by 80-90% and weight by about 70%, so little land is needed.
• Kills pathogens; suitable for hospital and hazardous waste.
• Heat can be recovered to generate steam or electricity.
• Can be located near the city, reducing transport; no odour or fly nuisance when operated properly.

Demerits

• High capital, operating and maintenance costs; needs skilled operators.
• Air pollution (dioxins, fly ash, SO₂, NOx) unless costly gas cleaning is provided.
• Not suitable for wet waste with a high organic content and low calorific value, as in Nepal (it needs auxiliary fuel).
• The ash still needs disposal, and non-combustibles (glass, metals) remain.