Rifiuti da centrali termoelettriche - ARPAL

PHARE TWINNING PROJECT RO2004/IB/EN-07 GUIDELINES ON INDUSTRIAL - THERMOELECTRIC PLANTS XX
degree of co-combustion. The quality of residues and by-products has two aspects – technical and
environmental quality:
• technical quality is the expression of various parameters, which together determine, to a large extent,
the applicability of the by-product. Apart from the purely technological parameters (e.g. stiffness, porosity,
particle size, moisture content), the contents of elements such as chloride, phosphorus, sulphate and
carbon are also important. This applies especially to ashes in concrete and cement. Technical
requirements will normally be issued by the (association of) construction industry. As the composition of
the ash can be different than without secondary fuel, valorisation can be a problem. (not all the secondary
fuels are normally EN-450 on ash in concrete
• environmental quality of the by-product is the expression of how heavy metals can leach from the
product in which they are applied, to the environment. Leaching characteristics determine, apart from the
technical properties, if the by-products are allowed to be applied for the products they are used for.
The impact of co-combustion on the by-product quality has been extensively investigated and reported in
some countries. Given the high removal rates of ESP, more than 99 % of the elements are found in the
ashes. Generally, changes in the composition of the fuel will result in changes in the composition of ashes
with the same magnitude. More specifically, elements that do not vaporise in the combustion process will
have the same concentration in all ash types. For more volatile elements, however, redistribution takes
place in the sense that they will be found more in fly ash and flue-gases upstream from the ESP than
elements that do not vaporise.
The conclusion is, ash composition in the event of co-combustion will change correspondingly with other
compositions of the secondary fuels. The elemental composition of the by-products can be predicted to an
extent that it is possible to determine the margins of which, when and to what quantities secondary fuels
can be co-combusted.
Ash composition, in the case of co-combustion, will change correspondingly with other compositions of the
secondary fuel. The elemental composition of the by-products can be predicted to such an extent that it is
possible to determine the margins of which, when, and to what quantities secondary fuel can be cocombusted.
Heavy metals (some less, some more) have the risk of leaching into the environment after they have been
exposed to water for a very long time. Leaching characteristics are less important for fly ash when it is used
in immobilised applications in the cement and concrete industry.
92