Rifiuti da centrali termoelettriche - ARPAL

PHARE TWINNING PROJECT RO2004/IB/EN-07 GUIDELINES ON INDUSTRIAL - THERMOELECTRIC PLANTS XX
Combustion residues (introduction)
A lot of attention has already been paid by industry to the utilisation of combustion residues and byproducts,
instead of just depositing them in landfills.
Utilisation and re-use is, therefore, the best available option and is a priority. There are tens of different
utilisation possibilities for different by-products. Each different utilisation option has different specific criteria
for the quality of ash it needs. It is impossible to cover all of these criteria. The quality criteria are usually
connected to the structural properties of the ash and the content of any harmful substances, such as the
amount of unburned coal in the ash, the solubility of heavy metals, etc.
The carbon rich ash can be recovered from ash streams. This produces a carbon rich ash that can be
recycled to the boiler to recover the energy in the carbon and a lower carbon ash stream that is less
restricted in terms of options for beneficial re-use.
The end-product of the wet scrubbing technique is gypsum, which is a commercial product for the plant. It
can be sold and used instead of natural gypsum. FGD sludges can be integrated in an FGD process byproduct
(gypsum) in the limits allowed. The sludges can be re-injected into the furnace when FGD and
SCR techniques are applied. Practically most of the gypsum produced in power plants is utilised in the
plasterboard industry. The purity of gypsum limits the amount of limestone that can be fed into the process.
The end-product of semi-dry desulphurisation processes is used in different construction purposes instead
of natural minerals, such as in road construction, for earthworks of composting and storage fields, for the
filling of mine pits, and for excavation dams in watertight construction.
Water and waste water treatment from coal and lignite
A variety of waste water types is generated by operating coal- and lignite-fired combustion plants. The
techniques for waste water treatment are applied to a large extent for the purification of waste water from
coal- and lignite-fired plants.
Managing the run-off water from coal yards, slag piles and by-product storage needs special attention.
Before discharging surplus water it must be safeguarded by treatment and monitoring so that the
applicable pollution limits are met. Dilution by fresh water to meet the limits is not acceptable.
Combustion residues and by-products treatment (Coal)
When coal is burned, most of the mineral matter is captured and removed as solid material at various
places in the system, such as at coal mills, at the bottom of the boiler, in the economiser flue-gas cleaning
system and in the stack. Bottom ash is recovered from all types of coal- and lignite-fired combustion
plants, although the percentage of total ash it accounts for varies.
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