Page 211 - Materials Chemistry, Second Edition

EXERGY ANALYSIS AND ITS CONNECTION TO LIFE CYCLE ASSESSMENT 197

value of fuels; since exergy can be used for both fuel and non-fuel resources
and can play an important role in the quantification of resource depletion in
fuel chains. The results show that vehicles with a compressed hydrogen stor-
age system are the most exergy efficient on a MJ/km basis.
Boyano et ah (2011) apply exergoenvironmental analysis to a steam methane
reforming process for hydrogen production. Exergoenvironmental analysis is
a combination of exergy analysis and environmental assessment, in which the
environmental impacts obtained by LCA or other environmental assessment
tools are apportioned to the exergy streams. The results point out the main
components with the highest environmental impacts and possible improve-
ments associated with these components. The results describe the environ-
mental impacts associated with energy conversion systems at the component
level, and provide useful information for designing systems with a lower
overall environmental impact. Also, components in which chemical reactions
occur are observed to have higher exergy destructions than other components.
The overall environmental impact can be reduced by decreasing the exergy
destructions within components, which usually requires the use of efficient
modern equipment, expensive materials and efficient designs.
Granovskii et ah (2007) use exergetic life cycle assessment to evaluate the
exergy efficiency, economic effectiveness and environmental impact of pro-
ducing hydrogen using wind and solar energy in place of fossil fuels. In that
work, exergy efficiencies and greenhouse gas and air pollution emissions are
evaluated for all process steps, including crude oil and natural gas pipeline
transportation, crude oil distillation and natural gas reforming, wind and solar
electricity generation, hydrogen production through water electrolysis, and
gasoline and hydrogen distribution and utilization. The use of wind power to
produce hydrogen via electrolysis, and its application in a fuel cell vehicle, is
seen to exhibit the lowest rates of fossil fuel and mineral resource consump-
tion. The authors suggest that "renewable" hydrogen represents a potential
long-term solution to many environmental problems.
Peiro et al. (2010) assess the life cycle of biodiesel from used cooking oil. The
production of biodiesel consists of four stages: collection of used cooking oil,
pre-treatment, delivery and transesterification. The assessment uses LCA to
evaluate environmental impacts and ExLCA to account for the exergy input
to the system. The results demonstrate that the transesterification stage causes
68% of the total environmental impact. It is also noted that uranium and natu-
ral gas are the major exergy inputs.
Beccali et ah (2003) apply exergy analysis with LCA to conduct an exergetic
life cycle assessment of plaster materials. In that work, an exergy balance is
used to calculate the exergy losses and efficiencies for each stage of the exam-
ined processes: resource extraction, material processing, transport and prod-
uct manufacturing. The authors state that determining the overall destroyed
exergy provides not only a measure of resource depletion but also the most
suitable criterion to reduce the exergy losses and to improve the technologi-
cal efficiency of the industrial production system. They also point out that an
economic evaluation, in conjunction with the ExLCA approach, represents a