school energy&environment

Incineration

Incineration, with energy recovery (Waste to Energy systems) is another solution to dispose of waste and consists in the combustion of waste in order to:

• decrease the volume and weight of the material; to completely oxidize the waste into CO₂ and H₂O;
• recover the energy content of the waste;
• sterilize the residues.

The characteristics of waste produced in our homes is such that other fuel is not required for its combustion, the waste that is fed into the incinerators is sufficient, alone, for the combustion. What happens to the waste during the process? The carbon, hydrogen and sulphur content of the waste is oxidized forming CO₂, H₂O and SO₂. The humidity in the waste is transformed into steam, while the presence of halogens (Cl, F, Br) and Nitrogen produce acid substances and Nitrogen oxide (NO_x) respectively. Lastly the metals may undergo phenomena of volatilization and inert matter becomes slag. A simplified Waste to Energy plant includes a front pit, i.e. a separate area where the waste arrives that limits the spread of bad odours, an accumulation and mixing pit, where the waste is dumped and the incinerator. Incineration provides a series of advantages among which maximum reduction of the volume of the waste and energy recovery, but also a series of disadvantages that involve numerous problems, such as control of the polluting substances produced during combustion, disposal of the residues and a particularly complex management. Even though in Italy this solution has often been prevented and is scarcely utilized (only 19% of the waste at present is incinerated), in Europe it is a widely prevalent type of plant solution and many cities use the energy produced by their waste, in order to guarantee operation of their systems.