Page 137 - Synthetic Fuels Handbook

FUELS FROM TAR SAND BITUMEN 123

the Suncor operation, bitumen conversion to liquids is on the order of more than 75 percent
with fluid coking giving a generally higher yield of liquids compared to delayed coking.
The remainder appears as coke (approximately 15 percent by weight) and gases.
The Suncor plant (in operation since 1967) involves a delayed coking technique fol-
lowed by hydrotreating of the distillates to produce synthetic crude oil that has proper-
ties that are substantially different from the original bitumen (Table 4.4). The selection of
delayed coking over less severe thermal processes, such as visbreaking, was based (at the
time of planning, from 1960 to 1964) on the high yields of residuum produced in these
alternate processes. The yields of coke from the residuum would have exceeded the plant
fuel requirements, especially if the distillate had to be shipped elsewhere for hydrogen
treatment as well as a more favorable product distribution and properties. Alternate routes
for the disposal of the excess coke would be needed.
Fluid coking is a continuous process employing two vessels with fluid coke. It provides
a better yield of overhead products than delayed coking. Feed oil flows to the reactor vessel
where cracking and formation of coke occur; coke is combusted in the burner. Fluid-transfer
lines between these vessels provide the coke circulation necessary for heat balance. The
proportion of coke burned is just sufficient to satisfy heat losses and provide the heat for
the cracking reactions.
In the fluid-coking process, whole bitumen (or topped bitumen) is preheated and
sprayed into the reactor where it is thermally cracked in the fluidized coke bed at
temperatures typically between 510°C and 540°C (950°F and 1004°F) to produce light
products and coke. The coke is deposited on the fluidized coke particles while the
light products pass overhead to a scrubbing section in which any high-boiling products
are condensed and recombined with the reactor fresh feed. The uncondensed scrub-
ber overhead passes into a fractionator in which liquid products of suitable boiling
ranges for downstream hydrotreating are withdrawn. Cracked reactor gases (contain-
ing butanes and lower molecular weight hydrocarbon gases) pass overhead to a gas
recovery section. The propane material ultimately flows to the refinery gas system and
the condensed butane and butenes may (subject to vapor pressure limitations) be com-
bined with the synthetic crude. The heat necessary to vaporize the feed and to supply
the heat of reaction is supplied by hot coke which is circulated back to the reactor from
the coke heater. Excess coke that has formed from the fresh feed and deposited on hot
circulating coke in the fluidized reactor bed is withdrawn (after steam stripping) from
the bottom of the reactor.
Sulfur is distributed throughout the boiling range of the delayed coker distillate, as with
distillates from direct coking. Nitrogen is more heavily concentrated in the higher boiling
fractions but is present in most of the distillate fractions. Raw coker naphtha contains sig-
nificant quantities of olefins and diolefins that must be saturated by downstream hydrotreat-
ing. The gas oil has a high aromatic content typical of coker gas oils.
In addition to Suncor and Syncrude, Shell Canada Ltd. has also commenced operations in
the Athabasca tar sand through its Athabasca Oil Sands Project; the project is a joint venture
that consists of the Albian Sands Muskeg River Mine, the Shell Scotford Upgrader, and the
Corridor Pipeline. The joint venture currently consists of Shell Canada Ltd. (60 percent),
Chevron Canada Ltd. (20 percent), and Western Oil Sands LP (20 percent). Recently, Western
Oil Sands LP has been purchased by Marathon Oil Corp.
In April 2003, the project commenced fully integrated operations and by April 2004,
production capacity began to consistently exceed the project’s daily design rate and at the
end of 2005 daily production averaged 160,000 per day. Currently, the design capacity of
155,000 bbl/day of bitumen is being increased to 180,000 to 200,000 bbl/day. By 2010,
planned expansion are expected to further increase bitumen throughputs by approxi-
mately 90,000 bbl/day, raising total expected production to 270,000 and 290,000 bbl/day.
At the end of the expansion, the production is projected to be on the order of 525,000 bbl/day