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etc. [12]. |
The ratio of the sum of energy burdens of a particular product to |
its energy content is defined as the energy intensity of that pro- |
duct. Note that the inverse of energy intensity of a product repre- |
sents its product-specific efficiency. In the current study, a process- |
based energy allocation was employed, which was reported in |
Elgowainy et al. [12]. |
LCA of petroleum products accounts for energy use and emis- |
sions associated with all stages in the fuel cycle, including crude |
recovery and transportation, fuel production, transportation, dis- |
tribution and combustion of the fuel by end-use application |
[9,12]. Furthermore, allocation of energy use and emissions bur- |
dens among co-products was performed by utilizing product- |
specific efficiencies and process fuel shares [9,12]. This protocol |
was followed along each stage of the product life-cycle. Key |
parameters for upstream energy efficiencies and emissions associ- |
ated with recovery, processing and transportation of various crude |
inputs, NG and electricity generation are presented in Table S4, as |
well as the references of the parameters. Crude oil, NG, and elec- |
tricity generation mixes for US refineries are based on 2010 data |
to match refinery LP modeling data inputs. The EU parameters in |
Table S4 are based on data reported by JRC and Eurostat of the |
European Commission [3,13]. GREET was populated with these |
US and EU parameters (Table S4) to compare life-cycle energy |
and GHG intensities of petroleum products from US and EU |
refineries. |
A notable difference between US and EU crude recovery GHG |
emissions estimates is the magnitude of associated methane |
(CH4) emissions. This is attributed to the difference in methodolo- |
gies used to estimate CH4 emissions. For the US, the GREET model |
estimates CH4 emissions based on the flaring emissions from satel- |
lite data using a 5:1 ratio of flared to vented associated gas [22]. On |
the other hand, the JRC study relies on a report by the International |
Association of Oil and Gas Producers (OGP), which collected emis- |
sions data from OGP members [23]. Another key difference is the |
share of oil sands in crude feed to US refineries since GHG intensi- |
ties of oil sands crude are typically higher compared to conven- |
tional crude (see Fig. S4). Electricity GHG intensity is decided |
primarily by the electricity generation mix. Compared to the US, |
the GHG emission intensity of EU-generated electricity is signifi- |
cantly lower, mostly due to the lower share of coal power genera- |
tion and higher share of nuclear and renewable power generation |
in the EU mix. GHG emission factors for fuel combustion are fairly |
consistent between the US and EU, except for diesel. This differ- |
ence is due to the lower carbon content (on a mass basis) of EU die- |
sel compared to US diesel (Table S5). |
3. Results |
3.1. Overall refinery efficiency |
Fig. 1 presents the grouping of US and EU refineries using the |
parametric assumptions described above. HP yields and crude |
input |
API |
gravity |
are |
plotted |
to |
show |
their |
relevance |
in |
gLHV ¼ |
P |
nðPn LHVnÞ |
P |
mðCm LHVmÞ þ P |
0ðOIo LHVoÞ þ NGpurchased;LHV þ H2;purchased;LHV þ Electricitypurchased |
ð1Þ |
Fig. 1. Crude API gravity and heavy product yield of the studied US and EU |
refineries (The yield of heavy products, such as residual fuel oil, pet coke, asphalt, |
slurry oil and reduced crude, is calculated as a share of all energy products by |
energy value). |
294 |
J. Han et al. / Fuel 157 (2015) 292–298 |
categorizing refineries. Filled shapes represent US refineries, while |
unfilled shapes represent EU refineries. These results show that |
almost all Low API and High API/Low HP refineries are present |
within the US, rather than the EU Conversely, almost all EU refiner- |
ies form part of the High API/High HP group. For all subsequent |
results, comparing the Low API group with the High API/Low HP |
highlights the impact of crude API gravity, while comparing the |
High API/Low HP group with the High API/High HP group highlights |
the impact of heavy product yield. |
Fig. 2 illustrates the overall refinery efficiency in each of the |
three refinery groups. The bottom, mid and top of the boxes in |
Fig. 2 represent the 25th percentile, production-weighted average |
and 75th percentile, respectively, while the ends of the error bars |
represent the 10th and 90th percentiles. These results suggest |
strong impacts of API gravity and HP yield on overall refinery effi- |
ciency. This can be rationalized by the installed capacity (MJ |
throughput/MJ crude inputs) of deep conversion units, such as cok- |
ers and catalytic crackers, in each group (see Table S3). The Low API |
group has a much larger installed capacity of deep conversion units |
then the other groups. On the other hand, the High API/High HP |
group has a negligible capacity of cokers and hydrocrackers. |
These conversion units are more energy-intensive than other pro- |
cess units within refineries, and thus consume significant amount |
of utilities (heat and electricity) and hydrogen. |
Hydrogen is highly GHG-intensive, depending on the source. |
Thus, the amount and source of hydrogen consumption are key |
LCA parameters. Fig. 3 illustrates that on a MJ/MJ crude basis, the |
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