Page 38 - Materials Chemistry, Second Edition

A N OVERVIEW OF THE LIFE CYCLE ASSESSMENT METHOD 19

From other To other
unit processes unit processes
From the To the
environment environment

Figure 2.2 General template of a unit process. The process (grey rectangle) is considered as a
black box, having inputs (left-hand side) and outputs (right-hand side) from and to other unit
process (top arrows) and from and to the environment (bottom arrows).

Semi-
L conductor
production
TV
production

Electricity TV use
production

Figure 2.3 Fragment of a simplified flow diagram for an LCA on television (TV) sets. Because
the purpose is to show how unit process are connected, only the flows from and to other unit
processes are displayed, and flows from and to the environment are hidden. All transport,
packaging, etc. has been left out as well.

biotic resources, and land). Outputs come in several types as well: again prod-
ucts (including components, materials, and services), waste for treatment, and
residuals to the environment (including pollutants to air, water, and soil, waste
heat, and noise); see Figure 2.2.
Unit processes form the building blocks of an LCA. This is because products
are not harmful for the environment as such, except for the processes involved
in products. Producing, using, and disposing products creates the burden to
the environment. Therefore, these processes assume a central position in LCA.
The essential feature of LCA in which it distinguishes itself from the analysis
of an industrial or agricultural process is that it connects different unit process
into a system. A flow diagram is a graphical representations of the system com-
prised of connected unit processes. Figure 2.3 show a fragment of such a flow
diagram.
As we can see, some unit processes are connected with one another in
simple upstream-downstream connections, e.g., TV production is upstream
connected to semi-conductor production. But there are also more complicated
connections, e.g., electricity linking to different parts of the system, and recy-
cling feeding back to production. Flow diagrams are in fact huge webs of inter-
connected unit processes. In the present era of digital databases, LCA studies
can easily comprise several thousands of unit processes.