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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 |