Page 132 - Materials Chemistry, Second Edition

116 3 Life Cycle Inventory Analysis

• Since the base system generates 14 MJ electricity by incineration, this amount
does not need to be made available otherwise. Therefore the environmental loads
for an (EU-mix) electricity supply of 14 MJ are balanced and credited to the base
system.
• Likewise, 80 MJ heat result from incineration. Again an equivalent system has
to be modelled, for example, the heat supply by incineration of light fuel oil in a
defined plant. These environmental loads will be balanced and also credited to
the base system.
The treatment of the outputs from waste treatment of products under consideration
of OLR often leads to large systems that imply an elaborate modelling. Therefore a
credit entry by means of system equivalence is widely applied.
In many LCAs the system modelling under consideration of equivalence systems
(credit-entry method) is used in the same sense as ‘system expansion’ avoiding
allocation. This is, however, not true; the system is rather treated as a ‘quasi-closed
system’, as such simplified, and all links to other systems, unavoidable in OLR, are
not considered.
3.3.5.2 Comparison of Different Options of Waste Disposal
LCAs are frequently employed to determine the environmentally most favourable
option of waste disposal. 118) In many waste disposal technologies usable energy
that can be used for the production of electricity and/or steam and hot water
for district heating is generated. 119) These added values have to be considered in
an LCA by credit entry or system expansion. 120) Added values may also occur for
landfill by capturing of landfill gas and for mechanical-biological waste treatment,
for example, by the production of agrarian gas.
The main idea of this system expansion (‘basket of benefit approach’) is the equal
benefit of the compared disposal routes. It is a prerequisite to a comparison of
systems, and by consequence the fU is mostly modified (inclusion of added values)
(see Section 2.2.5.3).
Figure 3.24 shows the examined system if the goal definition of the LCA aims
to find out which of the two systems, material recovery or incineration of waste
cardboard, is environmentally more friendly. The fU of the system in this case is:
‘Disposal of 100 kg cardboard’.
The system expansion conducted here is done according to the same logic as in
the previously discussed case of co-products. While system expansion is seldom
used for co-products, its application in the assessment of waste disposal systems
is common place. Here, no reasonable alternatives exist and the systems mostly
remain feasible.
Since a waste incineration with energy generation (system B) implies an added
value (14 MJ electricity, 80 MJ thermal energy per functional unit), these amounts
of energy have to be added to system A where no energy is formed. Assumptions

118) White, Franke and Hindle, 1995; Giegrich et al., 1999.
119) In summer spare energy can also be used for cooling, which unfortunately is rarely applied.
120) Fleischer, 1995; Fleischer and Schmidt, 1996.