Fig. 5 shows that the factors that have the greatest impact on
overall HDRD production cost are feedstock cost, hexane cost,
and capital recovery. In this case, the purchase cost of canola oil
was $0.526/L (in 2010 dollars) but contributed $0.535/L to the
overall HDRD production cost. This slight difference in magnitude
is due to several factors: mass lost during hydroprocessing in the
form of CO2 and propane, mass gained during hydroprocessing in
the form of hydrogen, and differences in density between vegetable
oil and HDRD. The hexane cost shown in Fig. 5 is the ‘‘topup’’
hexane that must be purchased because not all of the hexane
used in the process can be recycled. The Aspen Plus models built
in this study showed that approximately 97% of the hexane can be
recycled, but 3% is lost with the HDRD product stream and the fuel
gas stream that contains the lighter propane and CO2 components.
Although capital recovery is a significant cost factor, its influence
on a $/L basis rapidly declines with increasing plant size; for a
58 million L/year (1000 bbl/day) plant, capital recovery contributes
$0.295/L to the overall HDRD production cost but for a 290 million
L/year (5000 bbl/day) plant, capital recovery only contributes
$0.115/L to the overall HDRD production cost. However, beyond
a plant size of 290 million L/year (5000 bbl/day), increasing feedstock
transportation costs essentially balance any incremental
economy of scale benefits for capital costs.