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refineries |
was |
facilitated |
using |
Argonne |
National |
Laboratory’s Greenhouse gases, Regulated Emissions, and Energy |
use in Transportation (GREET™) model [19]. The GHG emissions |
calculation combines carbon dioxide, methane and nitrous oxide |
with their global warming potentials, which are 1, 25 and 298, |
respectively, as recommended by the latest Intergovernmental |
Panel on Climate Change for a 100-year time horizon [20]. |
2. Refinery modeling and analysis approach |
In the current study, refinery LP modeling was employed to |
simulate and compare the operations of 43 US and 17 EU refineries |
with individual processing capacity of over 100,000 bbl/day crude |
oil. Note that although the 17 EU refineries account for only 25% of |
the total EU refining capacity, their operational characteristics |
appear to be quite consistent with aggregate average EU refinery |
operations (see Table S1). |
The |
selected |
US |
refineries |
were |
located |
in |
Petroleum |
Administration for Defense Districts (PADDs) 1, 2, 3 and 5, while |
the selected EU refineries were located in the coastal regions of |
Europe. Refinery LP models typically maximize profit by determin- |
ing the optimal volumetric throughput and utility balance among |
various process units within a refinery under specific market and |
operation conditions [21]. The output files from LP model sim- |
ulations contain volumetric and mass flow rates associated with |
inputs and outputs of process units. Using this information, energy |
inputs and outputs can be calculated by using known heating val- |
ues of various stream components. |
In this study, we grouped the U.S and EU refineries described |
above into three different groups according to their average crude |
API gravity and HP yield. As shown in Fig. 1, refineries were |
J. Han et al. / Fuel 157 (2015) 292–298 |
293 |
categorized in the following manner: (1) Low API (API grav- |
ity < 29), (2) High API/Low HP (API gravity > 29 and HP < 0.22) |
and (3) High API/High HP (API gravity > 29 and HP > 0.22). |
Table S2 also shows the operational characteristics of refineries |
in each refinery group. Note the almost no overlaps in the key |
parameters between the Low API and High API/High HP group. |
Among the two High API groups, the Low HP group is clearly more |
resource-efficient than the High HP group. It also needs to be noted |
that assigning refineries to any of the three refinery groups is not |
intended to provide a statistical or physical classification among |
refineries; rather it is intended to examine the impacts of resource |
and energy efficiencies on life-cycle GHG emissions. Within each |
refinery group, three major metrics were evaluated for each refin- |
ery: overall refinery efficiency, product-specific refining efficiency |
and life-cycle GHG emissions intensity. Based on the volumetric |
amounts of refinery inputs and outputs, and purchased electricity |
energy |
estimated |
by |
the |
LP |
modeling, |
the |
overall |
refinery |
efficiency was estimated by dividing the total energy output by |
the total energy input on a lower heating value (LHV) basis |
(see Eq. (1)). |
where gLHV is the LHV-based overall efficiency of a refinery. Pn, Cm |
and OIoare the amounts of refining product n (e.g., gasoline, jet fuel, |
diesel, liquefied petroleum gas [LPG], RFO, pet coke), crude input |
m, and other input material o (e.g., normal butane, iso-butane, |
reformate, alkylate and natural gasoline) in barrels for liquid prod- |
ucts |
and |
tons |
for |
pet |
coke, |
respectively. |
NGpurchased;LHV |
and |
H2;purchased;LHV are the LHV-based energy of purchased natural gas |
(NG) and purchased H2, respectively. Electricitypurchased is the energy |
in purchased electricity. LHVm, LHVn, and LHVo are the LHVs of |
crude input m, refined product n, and other input material o, |
respectively, in MJ/barrel for liquid products and MJ/ton for pet |
coke. |
In order to calculate the GHG emissions intensity for each |
refined product, the product-specific efficiency and process fuel |
shares need to be determined. This determination is essential as |
each product pool is supplied from a different set of process units, |
each with different energy and emissions burdens (see Fig. S2). |
Since refinery inputs propagate through individual process units |
to final products via intermediate products, each intermediate or |
final product carries with it certain energy and emissions burdens |
of the total refinery inputs, such as crude, natural gas, electricity, |