Page 206 - Materials Chemistry, Second Edition

192 LIFE CYCLE ASSESSMENT HANDBOOK

8.4 Exergetic Life Cycle Assessment (ExLCA)

In this section, exergetic life cycle assessment is described, including discus-
sions of the following topics:

• Linkages between exergy analysis and LCA
• Rationale for ExLCA
• ExLCA approach and methodology
• Applications of ExLCA
• Advantages and benefits of ExLCA over LCA

8.4.1 Linkages between Exergy Analysis and LCA
Environmental impacts associated with systems or processes can often
be decreased by reducing exergy losses or, correspondingly, increasing
exergy efficiencies. Exergy analysis is primarily a powerful tool for improv-
ing the efficiency of processes and systems, particularly - but not neces-
sarily - energy-intensive ones. A measure that increases efficiency allows,
for the same products or services delivered, less resources (or exergy) to be
used. This, in turn, reduces the extraction from the environment of energy
resources, such as fossil fuels and uranium (Rosen, 2002). Increased exergy
efficiency also reduces the requirements associated with new facilities for
the production, transportation, transformation, and distribution of the
various energy forms, all of which impact the environment (Dincer, 2000;
Rosen, 2002).
Exergy losses occur during the lifetime of a product or a process. Reducing
these losses, particularly those due to the use of non-renewable energy forms,
helps improve sustainability. Figure 8.2 illustrates the relation between exergy
and sustainability and environmental impact. As exergy efficiency approaches
ideality (i.e. 100%), environmental impacts approach zero, because exergy is
converted from one form to another without any losses (consumptions or waste
emissions). Sustainability approaches zero as exergy efficiency approaches to

Environmental Sustainability
impact

0
Exergy efficiency (%)
Figure 8.2 Qualitative illustration of the relation between the environmental impact and
sustainability of a process, and its exergy efficiency (Rosen and Dincer, 2001).