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Among the major stages in the life-cycle of a petroleum fuel (crude
recovery, transportation, refining and fuel transportation, dis-
tribution and combustion), the largest GHG emissions source is
fuel combustion, which can be accurately estimated from the car-
bon content of the fuel. The next largest GHG emissions source for
desirable fuels (e.g., gasoline, diesel and jet) is the petroleum refin-
ing stage. Oil refineries process a slate of crude oils of different
qualities into multiple fuel products for various applications. In
order to accurately estimate variations in petroleum refinery effi-
ciency and GHG emissions, reliable information relating to overall
energy inputs and outputs is required for different crude types,
refinery configurations and product outputs. In addition, energy
inputs and GHG emissions at the refinery level need to be allocated
systematically among petroleum products in order to develop
accurate product-specific GHG emissions intensities.
Both crude quality and final production specification are key
drivers for refinery configuration, operations and ultimately, refin-
ing energy efficiency. For example, historically, crude inputs into
US refineries have typically been heavier (average API gravity of
30–32) than EU refineries (average API gravity of 36–37) [1,8].
In the former case, because crude inputs are heavier, more inten-
sive processing is required to produce gasoline and distillate. In
terms of market demands, non-transportation fuel oil demands
in the US (Fig. S1) are smaller than in the EU. Consequently, US
refineries produce a smaller share of residual fuel oil (RFO) than
EU refineries do, and thus are considered to be more resource effi-
cient. Since gasoline and diesel require significantly more process-
ing than heavy products, US refineries in general are more complex
and energy-intensive than EU refineries. On this basis, it is unsur-
prising that US refineries have larger deep conversion units such as
cokers and fluidized catalytic crackers (FCC) relative to other
regions
(Fig.
S3).
These
process
units
are
instrumental
in
converting heavy refinery intermediate streams into gasoline and
diesel and are typically energy-intensive; hence their impacts on
refining efficiency and life-cycle analysis GHG emissions can be
substantial [9].
Other studies have examined product-specific efficiencies and
GHG intensities of refined products and there is a wide variation
in the potential emissions due to differences in modeling metho-
dology and input data. Furuholt used data of eight general refining
processes in Norwegian refineries to allocate refining energy use
and emissions to gasoline and diesel [10]. Similarly, Wang et al.
used a detailed process-level approach for a notional refinery and
demonstrated the difference between various allocation metrics
(energy, market-value and mass) [11]. Recently, Elgowainy and
Forman et al. used a refinery Linear Programming (LP) model to
simulate operation of 43 large US refineries in order to estimate
life-cycle GHG emissions of major petroleum products such as
gasoline, diesel and jet fuels [9,12]. By covering 70% of the total
US refining capacity, they: (1) developed a correlation between
the overall efficiency of US refineries and the corresponding crude
quality, refinery complexity and product slate; (2) provided aver-
age and variations of product-specific efficiency and process fuel
shares for each refined product; and (3) examined the possible
impacts relating to changing crude slates, regional and seasonal
variation, changing gasoline-to-diesel (G/D) ratios and Gas to
Liquid (GTL) diesel blending on refinery and product-specific
efficiencies. A recent well-to-wheels study by the Joint Research
Centre (JRC) of the European Commission evaluated energy and
GHG emissions performance associated with various automotive
fuels and powertrains, including petroleum gasoline and diesel.
By considering a marginal approach (future reduction in gasoline
and diesel demand), JRC concluded that marginal diesel in the EU
is more energy- and GHG emission-intensive than marginal gaso-
line [13]. Other authors have performed individual refinery analy-
ses and incorporated these results into life-cycle analysis (LCA) for
multiple notional refinery configurations [14–18].
These studies only focused on a specific region or configurations
and considered only a limited range of crude quality and product
slates, which is not sufficient to fully understand the complex
interaction between crude quality, refinery configuration and yield
of gasoline and distillate on one hand, and the consequent life-
cycle GHG emissions on the other hand. These disparities between
previous studies suggest a need to use a large pool of refinery data
to potentially simplify general understanding of refinery GHG
emissions. Noting the impact of key refinery metrics such as API
gravity and heavy product (HP) yield (e.g., RFO, pet coke and
asphalt) could have on refinery efficiency and GHG emissions, we
analyzed results from LP modeling of 17 large EU refineries in addi-
tion to recently reported 43 US refineries [9,12] and grouped them
according to their crude API gravity and HP yields. Note that these
two parameters (API gravity and HP yield) were recently identified
by Elgowainy et al. [12] as the key parameters that determine a US
refinery’s overall energy efficiency [9,12]. In this study, API gravity
and HP are used to represent resource efficiency. By analyzing data
at the sub-process level in these 60 refineries, this study correlates
the crude API gravity and HP yields of different groups of refineries
with the product-specific energy efficiency for each refinery pro-
duct and presents previously unavailable life-cycle impacts of
refinery resource efficiency on product-specific and refinery-level
GHG emissions. The life-cycle analysis of petroleum fuels from
various