Page 167 - Materials Chemistry, Second Edition

152 A. Bjørn et al.

should always check the flow nomenclature of the software used (e.g. SimaPro,
GaBi or OpenLCA) and follow this when naming the flows of constructed unit
processes. Unit processes of LCI databases (see Table 9.5) are commonly inte-
grated into LCA software, which ensures that their flow names are correct.
LCA practitioners may face a situation where an LCA software has no name for
a given elementary flow or the CAS-number (Chemical Abstract System number—
a unique identifier for a chemical) of an emitted chemical does not exist in the list of
flow names in a software. In this case, the LCA practitioner should check if there is
a characterisation factor (CF) for the chemical in the LCIA method to be applied in
the ensuing LCIA step. If this is the case, the LCA practitioner should create a new
flow in the LCA software with a name identical to the name of the CF, so the
software can create the link. If there is no CF, the LCA practitioner can either
calculate the CF on his/her own when guidelines to do so exist (e.g. for the USEtox
model; see Chap. 40) or discuss the potential of that substance to contribute to the
total environmental impact and to the resulting interpretation of the results. In the
case of missing flows that are not elementary flows, these should also be created in
the LCA software and used to link processes together. For example, in the case of a
waste to treatment flow that is specific to the studied system (part of the foreground
system), and therefore not existing in the LCA software, this flow should be created
in the software and used to link the process having it as an output to the most
appropriate waste treatment process that is available.

9.5 Constructing the LCI Model
and Calculating LCI Results

When all unit processes have been constructed or collected from LCI databases the
LCA practitioner can construct the LCI model. Each unit process can be seen as a
‘building block’ in the LCI model, the ‘size’ of which is ultimately decided by the
study’s reference flow derived from the functional unit in the scope definition (see
Chap. 8). This is because the reference flow decides the quantity required of each
unit process-specific reference flow. In other words, each unit process must be
scaled to fit the LCI model. Figure 9.8 shows an example of how this is done
manually for a simplified system composed of just three unit processes each having
just 4 flows.
In Fig. 9.8, Process 1 is first scaled to match the reference flow of the study
(100 kg of Product X). After the scaling of Process 1, 200 kg of Product Y is
required, which Process 2 is scaled according to. This means that 240 kg of Product
Z is required, which Process 3 is scaled according to, etc. In practice, LCA software
can carry out the scaling automatically for the practitioner, when told what the
reference flow of a study is.
In practice, inventory modelling is normally performed using a dedicated soft-
ware which supports both the building of the product system model, connecting the