Page 138 - Synthetic Fuels Handbook

124 CHAPTER FOUR

of bitumen with a lease operating life of 22 years. Expended production of the in situ
projects at Foster Creek, MacKay River, and Christina Lake will provide a further 200,000
bbl/day of bitumen at the time of completion.
The Scotford Upgrader is located next to Shell Canada’s Scotford Refinery near Fort
Saskatchewan, Alberta where bitumen from the Muskeg River Mine is upgraded into syn-
thetic crude oil. A significant portion of the output is sold to the Scotford Refinery for
further processing.
In addition to the coking options, the LC-Fining ebullated-bed hydroconversion
process is used at both the Syncrude Mildred Lake upgrader and the Shell Scotford
Upgrader. The H-Oil ebullated-bed hydroconversion process is used at the Husky
Lloydminster Upgrader.

4.6.2 Secondary Upgrading
Catalytic hydrotreating is used for secondary upgrading to remove impurities and enhance
the quality of the final synthetic crude oil product.
In a typical catalytic hydrotreating unit, the feedstock is mixed with hydrogen, preheated
in a fired heater, and then charged under high pressure to a fixed-bed catalytic reactor.
Hydrotreating converts sulfur and nitrogen compounds present in the feedstock to hydrogen
sulfide and ammonia. Sour gases from the hydrotreater(s) are treated for use as plant fuel.
Hydrocracking may also be employed at this stage to improve product yield and quality.
Thus the primary liquid product (synthetic crude oil) is hydrotreated (secondary
upgrading) to remove sulfur and nitrogen (as hydrogen sulfide and ammonia, respec-
tively) and to hydrogenate the unsaturated sites exposed by the conversion process. It
may be necessary to employ separate hydrotreaters for light distillates and medium-
to-heavy fractions; for example, the heavier fractions require higher hydrogen partial
pressures and higher operating temperatures to achieve the desired degree of sulfur and
nitrogen removal. Commercial applications have therefore been based on the separate
treatment of two or three distillate fractions at the appropriate severity to achieve the
required product quality and process efficiency.
Hydrotreating is generally carried out in down-flow reactors containing a fixed bed of
cobalt-molybdate catalysts. The reactor effluents are stripped of the produced hydrogen
sulfide and ammonia. Any light ends are sent to the fuel gas system and the liquid products
are recombined to form synthetic crude oil.
Finishing and stabilisation (hydrodesulfurization and saturation) of the liquid products
is achieved by hydrotreating the liquid streams, as two or three separate streams (Speight,
1999 and references cited therein). This is necessary because of the variation in conditions
and catalysts necessary for treatment of a naphtha fraction relative to the conditions neces-
sary for treatment of gas oil. It is more efficient to treat the liquid product streams separately
and then to blend the finished liquids to a synthetic crude oil. In order to take advantage
of optimum operating conditions for various distillate fractions, the Suncor coker distillate
is treated as three separate fractions: naphtha, kerosene, and gas oil. In the operation used
by Syncrude, the bitumen products are separated into two distinct fractions: naphtha and
mixed gas oils. Each plant combines the hydrotreated fractions to form synthetic crude oil
that is then shipped by pipeline to a refinery.

4.6.3 Other Processes
Other processes which have also received some attention for bitumen upgrading include
partial upgrading (a form of thermal deasphalting), flexicoking, the Eureka process, and
various hydrocracking processes.