Waste to be incinerated is notably household and similar waste, sludge from wastewater treatment plants, healthcare waste and special industrial waste.
Incineration facilities are permit-holding classified installations as per sections 167c or 322b4 of the nomenclature relative to classified installations.
Different incineration processes are operated on an industrial scale. However, most household waste incinerators use grate furnaces.
- Grate furnaces. Waste is processed in relatively thin layers to facilitate the air supply required for the combustion. Grate furnaces, most commonly used in thermal treatment facilities, are characterised by a mobile grate through which waste is processed as it is burned. The combustion air arrives through this grate which mixes waste in order to ensure constant air renewal around the materials to be burned.
- Roller furnaces are made up of large rollers turning in the direction of the slope. These furnaces can be used for medium to high treatment capacity. There is also a system in which the furnace itself turns or oscillates around a slightly inclined axis.
- Fluidised bed furnace developed for the use of very poor quality fuels (peat, certain types of waste coal) has been adapted for household waste. These furnaces maintain the fuel in suspension, generally within a mass of inert products, using an air injection system at the bottom of the combustion chamber. Preliminary waste preparation is necessary to obtain constant particle size distribution. This process remains underused compared with grate furnaces.
- Pyrolysis and thermolysis. This is a thermal treatment of waste, in the absence of oxygen, at a temperature of approximately 500°C. Waste must be crushed before treatment. This process generates a combustible by-product which should be treated accordingly. This technique reduces the volume of flue gases. In addition, the absence of oxygen limits the formation of dioxins and furans in flue gases.
Special industrial waste is generally incinerated in a rotary furnace.
Thermal treatment, when combined with energy recovery, enables the waste-to-energy process by producing electricity and/or heat. Energy recovery can apply to all types of thermally treated waste.
Although only a recommendation, energy recovery is rapidly extending to new facilities.
In cement plants, it is possible to replace part of the fossil fuels (fuel oil, coal etc.) by waste with high calorific value. Bottom ash from household waste incineration represents 25 to 30% of the mass of household waste incinerated and 10% of the volume. French resources represent approximately 2.7 million tons per year (Ademe, 1999).
The use of this bottom ash in road engineering constitutes one of the main recovery outlets. Circular no. 94-IV-1 of 9 May 1994 classifies bottom ash from household waste incineration into three categories depending on its pollution potential:
- Bottom ash with low leachable fraction or ‘V’ category for ‘Recovery’.
- Intermediate bottom ash or ‘M’ category for ‘Maturation’.
- Bottom ash with high leachable fraction or ‘S’ category for ‘Permanent Storage’. The pollution potential of bottom ash from household waste incineration is determined by carrying out a leaching test as per standard XP X31-210 (May 1998).
2Economic and financial aspects 2
Incineration costs vary depending on:
- The technology used,
- The income generated by energy recovery,
- The nature of waste,
- The environmental standards applied. Their evolution is a key factor in cost evolution.
The thermal treatment of waste generates nuisances regulated by the legislation on classified installations:
Order of 20 September 2002 on incineration and co-incineration facilities for non-hazardous waste and incineration facilities for infectious healthcare waste, amended by the order of 10 February 2005 (Official Journal of 17/03/05)
Circular of 17 January 2005 relative to the treatment of flue gas purification residue from household waste incineration
See: Incineration section