Low Carbon Economy, 2010, 1, 86-91
doi:10.4236/lce.2010.12011 Published Online December 2010 (http://www.SciRP.org/journal/lce)
Environmental Sustainability Assessment of Electricity
from Fossil Fuel Combustion: Carbon Footprint
Jorge Cristóbal, Jonathan Albo, Angel Irabien
Universidad de Cantabria, Ingeniería Química y Química Inorgánica, Santander, Spain.
Received August 4th, 2010; revised September 10th, 2010; accepted October 8th, 2010.
ABSTRACT
Emissions of greenhouse gases from electricity production should be reduced since climate change has became a big
concern in developed countries. Carbon footprint is used as environmental index measuring the emissions that have
effect on global warming and shows that secondary footprint has an important relevance in the final emission factor. To
achieve sustainability in electricity production is required the consideration and evaluation of all relevant environ-
mental impacts at the same time. Reduction in CO 2 emissions is justified since clean combustion is achieved and global
warming is the main contributor to global impacts.
Keywords: Carbon Footprint, Environmental Sustainability Assessment, Fossil Fuels, Combustion, Environmental
Burden
1. Introduction
Climate change is a global problem that affects the whole
planet as one. Emissions from different countries con-
tribute the same to this environmental aspect defined as
the effect of anthropogenic emissions which enhance the
radioactive forcing of the atmosphere, causing the tem-
perature at the earth’s surface to rise [1]. Several gases
have influence in this impact, being carbon dioxide the
main contributor and the reference to measure the effect
of the rest gases. Developed countries are especially
concerned about reducing greenhouse gas (GHG) emis-
sions as it was established in the Kyoto protocol and fur-
ther European policies for energy [2].
Energy demand and transport needs are the origin of
the main amount of GHG. Reductions in these two ac-
tivities are called to be the way to achieve the levels
agreed internationally. 62% of the world electricity
comes from hard coal (HC) and natural gas (NG) com-
bustion and in the case of Spain 55% [3 ] so in this study
both electricity generation technologies carbon footprint
(CFP) are compared. Just environmental aspects would
be taken into acco unt but the framework that justifies the
comparison is much wider since the use of one raw ma-
terial or another has social and economic implications.
Last year trends in the Spanish electric mix show a
growth in the use of natural gas and a decrease in the use
of coal. This fact has clear social consequences due to the
decrease in the employment of regional mining sector,
very important in the north of Spain. Impacts of unem-
ployment could be measured on society as a whole or on
the individual persons as proposed by Jorgensen et al. [4].
Social life cycle assessment is still in his earlier phases
and the trade-offs with the env ironmental dimensions are
not clear enough. Furthermore European policies have
the objective of supply security and in the case of Spain
coal is an important so urce since it is the only raw mate-
rial present in the country, being dependent from abroad
for all other combustibles.
Environmental sustainability concerns the environ-
mental impact of inputs (resource usage) and outputs
(emissions, effluents and waste) of the process under
study and is evaluated by indexes to facilitate and sup-
port decision making and policies. They can be used to
compare different technologies because they reduce the
complexity in the analysis taking into account an impor-
tant number of chemical substances. CFP is a subset of
the environmental sustainability indexes that measure all
GHG produced (global warming potential impact cate-
gory) and has units of tonnes (or kg) of carbon dioxide
equivalent. It has been largely discussed the use of this
index to decision making processes because it restricts
the information and can lead to misleading interpretation
of data. Is global warming (GW) the main global impact?

Environmental Sustainability Assessment of Electricity from Fossil Fuel Combustion: Carbon Footprint 87
Is more important than ozone depletion (OD) or atmos-
pheric acidification (AA)? Achieving sustainability in
electricity production requires the consideration and
evaluation of all relevant environmental impacts at the
same time. But the use of CFP is justified from the eco-
nomic point of view. Since the Kyoto Protocol, carbon
credits came into existence; is a tradable permit scheme
that creates a market for reducing GHG emissions by
giving a monetary value to the cost of polluting the air
[5]. Three market-based mechanisms are set up to help
countries to achieve their reductions:
 International em issi on tradi ng–carbon credit ma rket
 Clean development mechanisms
 Joint implementation
The perspective of the Life Cycle Assessment (LCA)
permits evaluate the influence of all processes considered
in the system boundaries of different technologies and
evaluate alternatives to reduce emissions. CFP is made
up of the sum of two parts: the primary footprint meas-
uring direct emissions of CO2 from burning fossil fuels
and the secondary footprint measuring indirect emissions
from the whole lifecycle of the product.
2. Methodology
LCA was used as the main methodology to obtain emis-
sion values. It was done following the principles and
stages proposed by ISO in the normalization procedure
14040 [6]. It assesses all steps involved in electricity
generation as is showed in Figure 1 where system
boundaries are represented. A cradle to gate analysis
would be carried out considering that relative contribu-
tions of the downstream processes are expected to be
independent of the used technology. Neither decommis-
sioning of the plant nor disposal of the materials were
considered due to lack of data. For this study the func-
tional unit was established as the production of 1 kWh as
proposed by Gagnon et al. [7] being inappropriate com-
parisons of systems based upon installed capacity .
For the analysis, both life cycles have been divided in
upstream processes (that includes exploration and pro-
duction/extraction of the fossil fuel, transport to the
power plant and construction of the infrastructure to
transport it), constru ction of the power plant, combustion
at plant (including all the materials needed to the correct
functioning) and the disposal of waste and wastewater
from the combustion as it is showed in Figure 2.
SimaPro 7.2® software was used as LCA tool using
the Ecoinven t [8] databa se that refers data to Sp ain in the
year 2000. It assumes that technology is the average in-
stalled in Spain. The average net efficiency of Spanish
HC power plants is 35,8% and the assumed capacity is
450 MW. On the other hand, average installation tech-
nology for the NG plant is 100MW, with an efficiency of
47%.
Figure 1. LCA system boundar i es.

Environmental Sustainability Assessment of Electricity from Fossil Fuel Combustion: Carbon Footprint 88
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 sub-
stance 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 in-
direct CO2 emissions form the whole life cycle of the
product being more difficult to control and quantify. Re-
ducing options for diffuse emissions are focused on
avoiding them controlling transport distances and extrac-
tion practices.
3. Results
As it was expected the primary footprint is the main con-
tributor 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 pro-
duced following th e results expressed in Gagnon et al. [7]
and Evans et al. [10]. Secondary footprint has an impor-
tant 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 de-
pendent of gas importation from Africa and Europe in
contrast with hard coal where 33% is extracted from na-
tional reserves [11]. When using national hard coal, the
carbon footprint due to transport becomes negligible be-
cause usually are installed mine mouth plants. The influ-
ence 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 im-
ported from distances higher than 8200 kilometres would
equal the emissions derived from the combustion of na-
tional 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-com-
bustion 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].

Environmental Sustainability Assessment of Electricity from Fossil Fuel Combustion: Carbon Footprint 89
Figure 3. Influence of transport in the carbon footprint.
Table 1. Carbon footprint potency factors proposed by
IChemE.
Substance Potency Factor (PF)
Carbon dioxide 1
Carbon monoxide 3
Carbon tetrachloride (CFC-10) 1400
Chlorodifluoromethane, R22 1700
Chloroform 4
Chloropentafluoroethane, R115 9300
Dichlorodifluoromethane, R12 8500
Dichlorotetrafluoroethane, R114 9300
Difluoroethane 140
Hexafluoroethane 9200
Methane 21
Methylene chloride 9
Nitrous Oxide 310
Nitrogen Oxides (NOx) 40
Pentafluoroethane, R125 2800
Perfluoromethane 6500
Tetrafluoroethane 1300
Trichloroethane (1,1,1) 110
Trichlorofluoromethane, R11 4000
Trichlorotrifluoroethane, R113 5000
Trifluoroethane, R143a 3800
Trifluoromethane, R23 11700
Volatile Organic Compounds 11
CFP show that HC present a higher value than NG but
if political problems with the actual gas suppliers or the
resource depletion force the importation of NG from a
further country, national HC could be a better solution.
In the Spanish context proposed, average technology
in 2000, speaking just about CFP would hide the real
problem of emissions and global impacts. Through the
application of environmental burdens sustainability in-
dexes it would be proved that the biggest impacts are
produced by sulphur dioxide and nitrogen oxides, being
these substances a priority to the env ironmental pollution
control.
Normalization procedures based on the environmental
burdens given by the IChemE [13] are used in the present
paper. The normalized Environmental Burden (EB) is
calculated individually for each emitted substance (1),
weighted by a potency factor that transform the emission
to a reference substance and divided by the annual
threshold of the reference substance established in the
Annex II of the E-PRTR Regulation [14].
,,
1*
iN iNINr
EBW PF Th (1)
where EBi = ith environmental burden, WN = weight of
substance N emitted, including accidental and uninten-
tional emissions, PFi,N = potency factor of substance N
for ith EB, ThI,Nr = threshold value for the reference sub-
stance Nr of the impact category I.
Data from the HC combustion process are showed in
Table 2. The average desulfuration rate in data is 14%
and for denitrification the value is 8%. Atmospheric
Acidification is the impact category with the highest
value of the index. The main contributors to this value
are sulphur dioxide and nitrogen oxides. In the third
place appear carbon dioxide as the main contributor to
global warming. The desulfuration removal efficiency
should increase until 85% and the rate of denitrification

Environmental Sustainability Assessment of Electricity from Fossil Fuel Combustion: Carbon Footprint 90
Table 2. Environmental impact assessment for global impacts.
Substance Reference substance Emission Ton/TWhPF Th (Ton/year) EB
Sulfur dioxide 7.31E + 03 1 48,74
Nitrogen oxides 3.62E + 03 0,7 16,89
Hydrogen chloride 131 0.88 0.77
Hydrogen fluoride 42.30 1.6 0.45
Ammonia
Sulfur dioxide
0.94 1.88 1.18E – 02
AA
TOTAL SO2 eq. 1E + 04 1
150
66.86
Carbon dioxide 9.61E + 05 1 9.61
Nitrogen oxides 3.62E + 03 40 1,45
Dinitrogen monoxide 8.90 310 2.76E – 02
Carbon monoxide 81.3 3 2.44E – 03
Methane
Carbon dioxide
10.9 21 2.29E – 03
GW
TOTAL CO2 eq. 1.11E + 06 1
100000
11.09
Methane, 4Cl, CFC-10 2.29E – 04 1,1 0,26
Methane, Br3F, Halon 1301 2.97E – 06 10 2.97E – 02
Methane, BrCl2F, Halon 1211
CFC 11
3.76E – 06 3 1.13E – 02
OD
TOTAL CFC 11 eq. 2.93E – 04 1
0.001
0.29
until 50%, reducing EB under 9.61 to consider Global
Warming as the mayor impact. Just then CO2 would be
the next step in the reduction policy.
4. Conclusions
Reduction in GHG is a priority for Europ ean countries as
their strategies for energy show and quantitative indexes
are needed to support decision making. CFP measures
the emission of gases that a have an effect on global
warming and is useful to compare different technologies.
Results show that NG emits half of the GHG than HC to
produce the same amount of energy when comparing the
both life cycles.
The importance of the upstream processes is showed
in the analysis being transport a sig nificant contributor to
the CFP of energy production. In the scenario of the
study where all the HC burned in Spain would be na-
tional, being transport influence negligible, emissions of
GHG from NG tran sported 8200 Km would be compara-
ble to HC. If actual importing countries couldn’t provide
Spain with NG and other much further country should do
it, national coal would provide same energy with same
GHG emission. Then the social and economic implica-
tions would be an important advantage for the national
raw material.
As this study is focused on the environmental dimen-
sion, an assessment of all global atmospheric impacts,
using HC combustion data, show that atmospheric acidi-
fication has a higher impact index value due to the emis-
sion factor of SO2 and NOx being those substances a pri-
ority in a reduction policy. Carbon capture is justified
since clean combustion (denitrification and desulfuration)
is achieved and CO2 is the main contributor to global
impacts.
CFP was co mpared for both technolog ies and then ex-
panded on global atmospheric impacts for the HC case
but environmental sustainability can be assess through
many different indexes. The difficult issue is the election
of the correct index for the scope and boundaries of the
study.
5. Acknowledgements
This research was funded by the Spanish Ministry of
Science and Technology (Project C-CTM2006-00317 ).
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