Rifiuti da centrali termoelettriche - ARPAL

PHARE TWINNING PROJECT RO2004/IB/EN-07 GUIDELINES ON INDUSTRIAL - THERMOELECTRIC PLANTS XX
Bottom ash, however, applied for example as a layer under a road, can involve leaching of some elements
in the long term. A shift in microelemental composition and leaching may pose a constraint to the
application of bottom ash as a consequence of co-combustion.
Gypsum will hardly be affected by changing the composition of the fuel. There is no hazard of leaching, as
the product is applied principally inside buildings, where contact with water is not the issue. But according
to quality requierements, gypsum is normally washed before it leaves the power plant.
Filter ashes of pretreatment processes, such as gasification or CFBs, are generally more difficult to apply
and may have to be sent for disposal. Techniques to immobilise the microelements can open possibilities
for applications.
For an overall evaluation of the environmental impact of heavy metal concentrations, the immobilising and
stabilising of heavy metals in the residue should be taken into account as well as the calculation of the total
content. The extent of immobilisation can be calculated from the heavy metal concentrations in the eluate.
Follow table show the effect of cocombustion on combustion residues such as dry sorption residues and
coarse ash in comparison with regular fuel. It can be seen that the concentrations of Hg , Pb and Cd are
increased in the mixture fly ash dry sorption residue. Also, the concentrations of Pb, Zn, Cu and Cr are
increased in the coarse ash which makes material recovery impossible.
However, leaching behaviour was not notably influenced.
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