Page 84 - Materials Chemistry, Second Edition

68 3 Life Cycle Inventory Analysis

Exercise: Sample case for a calculation of CO -emissions
2
An energy concern supplies natural gas to its customers (original data).
The following figures are known (even though the unit kilowatt hour should only
be used for electricity, it is also applied in technical contexts, as in this case, to
indicate low and high heat values):

Natural gas Average Unit
component fraction
Methane CH 4 87.535 mol%
Ethane C H 5.545 mol%
2 6
Propane C H 8 2.000 mol%
3
i-Butane C H 0.248 mol%
4 10
n-Butane C H 10 0.351 mol%
4
i-Pentane C H 0.056 mol%
5 12
n-Pentane C H 12 0.004 mol%
5
Nitrogen N 3.260 mol%
2
Carbon dioxide CO 2 0.960 mol%
Other data Average value Unit
High heat value 11.580 kWh m −3
Low heat value 10.457 kWh m −3
Density 0.821 kg m −3
Calculate the CO emissions in g MJ −1 that are released due to the incineration
2
of the natural gas. Use the low heat value. Energy expenditure for extraction and
transport of the natural gas to the customer (upstream) is not considered here.

If detailed data procurement is possible, it should be made. As for data procured in
the factory, the primary data (sometimes called foreground data ) can be combined
26)
with an operational input–output analysis or be taken from it as the same data
are required at the process level. An operational input–output analysis, 27) however,
does not require an allocation of inventory parameters to particular products.
Besides, it should be considered that many unit processes do not refer to
industrial products as such, but to agri- or silvicultural processes or to those
of disposal or to those of use/consumption of a product. The latter depend on
consumers’ attitudes and behaviours in daily life, which is a field that has rarely
been investigated quantitatively.

26) According to our knowledge, a distinction between foreground and background data was first
made in a SETAC Europe Working Group on Life Cycle Inventory Analysis with Roland Clift as
chair (unpublished, about 1997).
27) Hulpke and Marsmann (1994), Schaltegger (1996), Schmidt and Schorb (1995), Finkbeiner,
Wiedemann and Saur (1998) and Rebitzer (2005).