Hydrocarbon Processing - June 2021 - 45

Catalysts
total feed, making the FCC processing in the AOR one of the
most challenging worldwide.
The feed characteristics in TABLE 1 from residual streams may
lead to the following FCCU limitations:
* Main air blower (MAB) or wet gas compressor
(WGC) capacities may be exceeded-in many FCC
operations, the Ni content of Ecat systematically grows,
making it necessary to use catalysts with improved
Ni trapping to avoid running into WGC constraints,
as Ni is known to produce hydrogen.
* Upper limits for regenerator temperature and stripping
efficiencies create bottlenecks and are strongly
interrelated with the coke remaining on the spent
catalyst. If the hardware in the regenerator or regenerator
design cannot cope with the temperature increase or
afterburn, this will also be a limiting factor.
* Bottom-of-the-barrel products (e.g., FCCU bottoms
product) have a limited market, either for sale to a coking
refinery or as one of a few different grades for coking.
RFCCU. AOR uses a proprietary RFCCUa
technology to convert
heavy, high molecular-weight and metals content feedstock
into higher value streams. This technology was originally
developed as a cost-effective, flexible and reliable means
to profit from market opportunities at times when it was crucial
to leverage the intrinsic potential of residuum feedstocks.
Various challenges posed by such feeds have been overcome as
detailed here, and innovations have been kept up-to-date. In
particular, the Atyrau proprietary RFCCUa
* A leading resid feed injector technologyc
is equipped with:
that ensures
appropriate feed distribution to promote vapor-phase
cracking, resulting in low coke and dry
gas make and superior liquid selectivity
that limits the burden on the WGC
* Mix temperature control (MTC) that
ensures riser temperature control
through quench to increase the C/O
ratio and displace the equilibrium
between catalytic and thermal
cracking to achieve better selectivities
offering
* A riser termination deviceg
high gas containment to limit
products degradation to light ends,
while being highly resilient to
transient phases
* Superior catalyst stripping with
structured packing to preserve the
valuable hydrocarbon material and
reduce the regeneration temperature
at low stripping steam rates.
More importantly, the RFCCU configuration
incorporates a two-stage catalyst regeneration
(FIG. 4) that minimizes catalyst
deactivation in the presence of metals to
maintain higher activity with more metals
on the catalyst, thereby reducing catalyst
replacement costs.
The first regeneration stage operates in
partial burn mode. High hydrogen content
molecules are burned in this stage, yielding water. The extent
of the regeneration is controlled to limit the temperature elevation
in the presence of water, which would otherwise cause
high hydrothermal deactivation of the catalyst. Moreover, in
the absence of excess oxygen, V oxidation cannot occur. This is
the first step in the mobility cycle of this molecule, which ultimately
leads to the collapse of the catalyst structure and drastic
reduction of its ability to convert the longer molecules inherently
present in FCC feeds.
The second regeneration stage operates in full burn mode
to restore the full catalyst potential. In this stage, the temperature
is further elevated, which is less detrimental to catalyst
activity than other solutions because water was removed with
flue gas in the first stage. Furthermore, in the absence of water,
the transformation of vanadium oxide to vanadic oxide is
largely impaired-once more this limits the V mobility, thus
inhibiting the noxious effects of this contaminant on catalyst.
It is worth noting that the two-stage scheme also rejects a
substantial portion of the regeneration heat as carbon monoxide
(CO) in the first stage, thus removing the necessity to
install a catalyst cooler at Atyrau despite the high concarbon
feedstock. This has a direct and positive impact on unit costs
and complexity of operation, as well as removing a burden for
maintenance. CO is subsequently oxidized to CO2
and noxious
components are captured or neutralized to ensure full compliance
with environmental norms. The expertise of various partnerships
are leveraged to systematically develop tailor-made,
highly energy efficient FCC flue gas treatments abiding with
the most stringent regulations worldwide. In the case of AOR,
an SCR DeNOx
, followed by a flue gas scrubber, was retained.
Additionally, state-of-the-art thermal integration was developed
specifically to accommodate changes
in feed composition, as well as the different
seasonal modes of operation required by
KMG, while maintaining a high energy efficiency
throughout all those cases.
For these reasons and owing to a strong
experience due to more than 40 designs performed
on feedstocks with concarbon higher
than 3 wt%, the RFCCUa
process provides
yields and performances with the flexibility
to process a wide range of feedstocks-from
gasoil through residue-in the same unit to
meet multiple product scenarios (max distillate,
max gasoline or max light olefins).
Finally, thanks to a robust design in conjunction
with a dedicated catalyst design,
AOR's FCCU succeeds in ensuring catalyst
circulation and is delivering expected performances
while processing high Fe content
feeds.
FIG. 4. Typical RFCCUa
arrangement
with dual-regeneration system.
RFCC catalyst design. For a given residue-containing
feedstock to be processed
in an FCCU, there is an optimized set of
operating conditions to maximize unit conversion
for a given FCC hardware design.
The mastery of such operating variables
handling, as well as continuous improveHydrocarbon
Processing | JUNE 2021 45
Hydrocarbon Processing - June 2021

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