Page 85 - Materials Chemistry, Second Edition

3.1 Basics 69

Material A
Pre-product Intermediate
Unit process x
Material B product

Figure 3.3 Branching due to several main inputs (multi-input process).

3.1.4
Flow Charts

Each box in a flow chart represents a unit process that requires full attention
from the LCA experts. Less important unit processes have already been cut-off in
the first phase (see Section 2.2.2.1). However, an iterative approach is preferable
whereby, in an LCI overview, unit processes to be neglected and side chains are first
determined with the use of estimated data. At the beginning of data acquisition at
the latest, a decision must be made concerning side chains to be cut-off and those
to be considered using estimated values.
The distinction between main and side chains cannot easily be made in complex
product systems. 28) Starting with the use phase the main chain follows the produc-
tion of the product upstream: production of product, production of intermediate
products, and finally reaches the extraction of raw material (the cradle). The disposal
chain runs in the opposite direction (‘downstream’) until the final destruction, for
example, by incineration (the grave). 29)
A flow chart as a ‘bead thread’ according to Figure 3.1 is too simplistic. Real flow
charts always produce branches. Two fundamental process types, multi-input and
multi-output processes, can be distinguished.
1. Several materials, pre-products and intermediate products, and so on, enter the
main chain by a unit process. This is called a multi-input process.InFigure3.3
a pre-product and two materials, A and B, enter the unit process X. A and B are

28) Fleischer and Hake (2002), Lichtenvort (2004) and Kougoulis (2007).
29) The methaphor cradle to grave has strongly contributed to a fundamental understanding of LCA,
see Chapter 1.