Figure 2. Carbon footprint.
CFP is a sub-set of data covered by a more complete
LCA, analysing just emissions that have an effect on
global warming and climate change. At least 13 different
methodologies for calculating the carbon footprint were
operative or under development in 2009 [9]. In this study
sustainability metrics proposed by IChemE are used. The
potency factors showed in Table 1 are based on a 100-
year integrated time horizons that transform the substance
to carbon dioxide equivalents.
CFP can be divided in two parts. On the one hand the
primary footprint that is a measure of direct emissions of
CO2 from burning fossil fuels. These punctual emissions
are more easily quantifiable because come from the stack
of the plant and options to reduce them are focused on
capturing substances before released to the atmosphere.
On the other hand secondary footprint measures the indirect
CO2 emissions form the whole life cycle of the
product being more difficult to control and quantify. Reducing
options for diffuse emissions are focused on
avoiding them controlling transport distances and extraction
practices.
3. Results
As it was expected the primary footprint is the main contributor
to the total emission. As Figure 2 shows the
amount of carbon dioxide equivalents by HC combustion
is two times the emitted in NG by kilowatt-hour produced
following the results expressed in Gagnon et al. [7]
and Evans et al. [10]. Secondary footprint has an important
relevance in the final emission counting up to 16%
and 12% in NG and HC respectively. Plant construction
and waste/wastewater treatments are negligible.
Using NG results a better option when CFP is assessed.
But as it was said before, Spain is a country totally dependent
of gas importation from Africa and Europe in
contrast with hard coal where 33% is extracted from national
reserves [11]. When using national hard coal, the
carbon footprint due to transport becomes negligible because
usually are installed mine mouth plants. The influence
of transport in GHG emissions is important and
reduction in the secondary footprint could be achieved
reducing or avoiding the long distance transport of raw
materials. As it is showed in Figure 3 the use of NG imported
from distances higher than 8200 kilometres would
equal the emissions derived from the combustion of national
HC.
To reduce the primary footprint several techniques are
being under research, focused on the Carbon Capture and
Storage (CCS) and the three most promising technologies
to capture CO2 from combustion process are post-combustion
capture, pre-combustion capture and oxy-fuel
combustion, being post-combustion based on chemical
absorption using monoethanolamine (MEA) as capture
solvent the most referred [12].