Environmental Engineering Reference
E NERGY R ECOVERY FROM W ASTE : C OMPARISON
OF DIFFERENT T ECHNOLOGY C OMBINATIONS
1 Lidia Lombardi and 2 Andrea Corti
1 Università degli Studi di Firenze, Via Santa Marta, 3, 50139 Firenze - Italy,
2 Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Siena,
Via Roma Siena - Italy.
Energy recovery from waste can follow several routes. The most common one is
waste direct combustion associated with conventional energy recovery in a steam turbine
cycle. The combustion can be applied directly to Municipal Solid Waste or can be
applied to a stream of selected waste obtained by means of mechanical sorting of
Municipal Solid Waste, using several technologies for the combustion, the most common
of which is mobile grate combustor.
Besides the direct combustion of waste, alternative possibilities for thermal treatment
are gasification and pyrolysis. These processes require being fed by a homogeneous
combustible fraction obtained by mechanical sorting and supply as output one or more
combustible streams, available for energy recovery.
When Municipal Solid Waste mechanical sorting is applied, besides the combustible
fraction stream, a humid fraction is also obtained, characterised by a high presence of
organic biodegradable fraction. At present the fate for this stream is biological aerobic
stabilisation, but another option, to push energy recovery also from this stream, is
biological anaerobic digestion, which can be applied through different technologies (wet
and dry digestion). Through this process a biogas with elevated content of methane can
be produced and supplied to engines for energy recovery.
The above-mentioned technologies can be combined in several schemes to optimise
the overall energy recovery. The combination of schemes will be analysed in this chapter
in reference to a study case characterised by an average waste material composition. The
comparison will be carried out using some indicators of the overall energy recovery for