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A life cycle assessment of tri-generation from biomass waste 219

Energy factors refer to the Cumulative Energy Demand (Frischknecht
et al., 2007a; Pre ` Product Ecology Consultants, 2012) method that enables
the estimation of the consumption of renewable (biomass, wind, solar, geo-
thermal, water) and nonrenewable (fossil, nuclear) energy sources. The
environmental characterization factors refer to the ILCD 2001 Midpoint
(European Commission—Joint Research Centre—Institute for Environ-
ment and Sustainability, 2012) impact assessment method, according to
the recommendations of the ILCD Handbook of the European Commission
(European Commission, DG Joint Research Centre, Institute for Environ-
ment and Sustainability, 2011).

2.2 Life cycle inventory
2.2.1 The tri-generation plant
The examined plant (Fig. 7.1) produces biogas from the anaerobic digestion
of agricultural waste and manure coming from the “agro-combined” of
Thibar. The biogas feeds an internal combustion engine that generates elec-
tricity and thermal energy for heating and cooling.
The biomass waste is transported to the plant with trucks for a distance of
5km (1). It is temporarily stored in a tank (2) and then goes to the anaerobic
digester (3), where the organic matter is decomposed by anaerobic micro-
organisms producing biogas. The biogas feeds a tri-generation plant for
energy production. In detail, the plant produces electricity, which is partially
used for the auxiliary consumptions and partially to feed the grid, and ther-
mal energy, used for heating (6) and cooling (7) production. The digestate
produced during the process is stored (4) before being disposed or further
treated for agricultural purposes (5) (distance from the plant to the final treat-
ments: 100km).
The plant manages 5900t/year of waste biomass and produces
3 3
193,680Nm /year of biogas (340Nm per ton of biomass) with a low cal-
3
orific value of 5.9kWh/Nm .
During the operation the tri-generation system (electrical efficiency:
1
37%) produces 422,800kWh of electricity and 571,356kWh of thermal
energy, of which half is used for the heating production and half by the
absorption chiller (energy efficiency ratio: 0.9), together with 923.33m 3
of water, to generate 257,119kWh of cooling.

1
The 10% of the electricity produced is used for the auxiliary consumptions.