Ultra-low-sulfur diesel vs ULSG

Ultra-low-sulfur diesel
https://en.wikipedia.org/wiki/Ultra-low-sulfur_diesel

Ultra Low Sulfur Gasoline (ULSG) of below 10ppm

The new regulations for diesel and gasoline both require that these fuels meet the American
Society for Testing Materials standard (ASTM D5453-00), which uses ultraviolet fluorescence to
measure sulphur concentrations in liquid hydrocarbons. Other specified methods may also be
acceptable (e.g. X-Ray spectrometry), however producers must contact Environment Canada
before using a different method. For further information on standards for testing sulphur
concentrations in diesel, please see:


ULSG Production
As Exhibit 15 suggests, reducing the sulfur content of gasoline calls for desulfurizing (in order of
priority) FCC naphtha, coker distillate (in deep conversion refineries), and straight run naphtha.
FCC naphtha, the main contributor to gasoline sulfur, can be desulfurized to < 10 ppm sulfur in a
suitably configured FCC naphtha hydrotreater. These units can be designed or upgraded to
achieve > 97% reduction in the sulfur content of FCC naphtha and can produce FCC naphtha with
sulfur content as low as 10 ppm. In conversion refineries, this step alone can suffice to meet
gasoline sulfur standards as low as 10 ppm.
Coker naphtha, produced in deep conversion refineries, is usually desulfurized either in the FCC
naphtha hydrotreater (for direct blending to gasoline) or in the naphtha hydrotreater, (for use as
reformer feed).
Straight run naphtha, from the crude distillation unit, is desulfurized in the isomerization unit
(an upgrading process, discussed in Section 4.1.3), if the refinery already has one. Otherwise,
and if necessary, straight run naphtha can be desulfurized in a dedicated (new) hydrotreater.
One other approach, though rare, deserves mention. A few large U.S. refineries have FCC feed
hydrotreaters that operate at exceptionally high severity (almost verging on hydrocracking). These
units accomplish such a high degree of FCC feed desulfurization that the FCC naphtha needs no
further desulfurization (i.e., no FCC naphtha hydrotreating) in order for the refinery’s gasoline pool
to meet a very stringent sulfur standard.

ULSD Production
As Exhibit 16 suggests, reducing the sulfur content of diesel calls for desulfurizing all of the primary
diesel fuel blendstocks: straight run kerosene and diesel, light cycle oil, coker distillate (in deep
conversion refineries), and hydrocracked distillate (in refineries with hydrocrackers).
The usual practice is to blend all of these streams and then desulfurize them in a single distillate
hydrotreater. Meeting a new, more stringent diesel sulfur standard involves replacing, expanding,
and/or retrofitting an existing distillate hydrotreater, depending on the specific capabilities of that
unit and the sulfur standard to be met.
Severe FCC hydrotreating, of the type discussed above, can substantially reduce the sulfur content
of FCC-produced light cycle oil, but not nearly enough to obviate the need for additional distillate
hydrotreating capability to meet more stringent diesel sulfur standards.