PAGE 15

Deep Conversion of Bottom Barrel

Streams – Residue Fluid Catalytic
Cracking (RFCC) Technologies
Marcio Wagner

Introduction Taking into account the current scenario and the

forecasts, is expected a great contribution of FCC
The downstream industry faces a transition period
units to the economic sustainability of down-
where the focus of the players is changing from
stream industry, mainly related to the maximiza-
transportation fuels to petrochemicals aiming to
tion of petrochemicals from bottom barrel
ensure maximum added value to processed crude
streams.
oils as well as to allow the growth of low carbon
energies in the global energetic matrix. Residue Fluid Catalytic Cracking Technolo-
gies
The growing market of petrochemicals have been
lead some refiners to look for a closer integration Residue upgrading technologies aim to raise the
between refining and petrochemicals assets aiming H/C ratio in the bottom barrel streams through
to reach more adherence with the market demand, hydrogen addition or carbon rejection. Among
improve revenues, and reduce operation costs. In the technologies that apply the carbon rejection
this business environment, flexible refining technol- principle, the Fluid Catalytic Cracking (FCC) is
ogies like Fluid Catalytic Cracking (FCC) reach one of the most widely employed and which add
highlighted position in the strategy of the refiners more value to the refiners. Figure 1 presents a
to reach competitiveness in the market. Recent simplified process scheme of a conventional fluid
technology developments like additive manufactur- catalytic cracking process.
ing (3 D printing) can deeply change the transpor-
The typical feed streams to fluid catalytic cracking
tation fuels demand as well as the growing practice
units are gas oils from vacuum distillation. Howev-
of home office like demonstrated in the current
er, some variations are found as the use of heavy
COVID 19 crisis, facing this scenario, the look for
coker naphtha, coker gas oils and deasphalted oil
alternatives to transportation fuels can be trans-
from solvent deasphalting units, according to the
formed in a survival question to refiners in middle
adopted refining scheme.
term and the petrochemicals can offer an interest-
ing alternative.

Figure 1 – Schematic Process Flow Diagram for a Typical Conventional Fluid Catalytic Cracking Unit (FCC)
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One variation of the fluid catalytic cracking that has In this case, the temperature of the regeneration
been widely applied in the last years is the Residue vessel can reach values close to 760 oC, leading
Fluid Catalytic Cracking (RFCC). In this case, the to higher risks of catalyst damage which is mini-
feed stream to the process is basically the bottom mized through catalyst cooler installation. The
stream from the atmospheric distillation column, option by the total combustion mode needs to
called atmospheric residue, that have high carbon consider the refinery thermal balance, once, in
residue and higher contaminants content like met- this case, will not the possibility to produce steam
als, nitrogen, and sulfur. in the CO boiler, furthermore, the higher tem-
peratures in the regenerator requires materials
Due to the feed stream characteristics, the residue
with noblest metallurgy, this raises significantly the
catalytic cracking units require design and optimiza-
installation costs of these units.
tion changes. The higher levels of residual carbon
in the feed stream lead to higher temperatures in As pointed earlier, the feed streams characteris-
the catalyst regeneration step and a lower catalyst tics to RFCC units require modifications when
circulation rate to keep the reactor in constant compared with the conventional fluid catalytic
temperature, this fact reduces the catalyst/oil ratio cracking. The presence of higher content of nitro-
that leads to a lower conversion and selectivity. To gen compounds leads to an accelerated process of
avoid these effects, the RFCC units normally rely catalyst deactivation through acid sites neutraliza-
on catalyst coolers, as presented in Figure 2. tion, the presence of metals like nickel, sodium,
and vanadium raise the coke deposition on the
Installation of catalyst cooler system raises the pro-
catalyst and lead to a higher production of hydro-
cess unit profitability through the total conversion
gen and gases, besides that, reduces the catalyst
enhancement and selectivity to noblest products as
lifecycle through the zeolitic matrix degradation.
propylene and naphtha against gases and coke pro-
Beyond these factors, heavier feed streams nor-
duction, furthermore, helps the refinery thermal
mally have high aromatics content that are refrac-
balance, once produces high-pressure steam. The
tory to the cracking reactions, leading to a higher
use of catalyst cooler is also necessary when the
coke deposition rate and lower conversion.
unit is designed to operate under total combustion
mode, in this case, the heat release rate is higher Due to this operation conditions, the residue fluid
due to the total burn of carbon to CO2, as pre- catalytic cracking units presents higher catalyst
sented below. consumption when compared with the conven-
tional process, this fact raises considerably the
C + ½ O2 CO (Partial Combustion) H = - 27
operational costs of the RFCC units. However,
kcal/mol
the most modern units have applied specific cata-
C + O2 CO2 (Total Combustion) H=- lysts to process residual feed streams, in this case,
94 kcal/mol

Figure 2 – Catalyst Cooler Process Arrangement for a Typical RFCC Unit

(Handbook of Petroleum Refining Processes, 2004)
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the catalyst has a higher porosity aiming to allow a Like to the conventional FCC units, the main op-
better adaptation to the high aromatics content, erational variables to RFCC units are the reaction
furthermore, the catalyst needs to have a higher temperature, normally considered in the highest
metals tolerance. point in the reactor (also called riser), feed
stream temperature, feed stream quality, feed
The control of contaminants content in the feed
stream flow rate and catalyst quality. It’s relevant
stream or his effects is a fundamental step to the
to quote that the conventional FCC units can
residue fluid catalytic cracking process. Sodium
process atmospheric residue as the feed stream,
content can be minimized through an adequate
however, it’s necessary to control the contami-
crude oil desalting process and the effects of nickel
nants content, mainly metals, which requires pro-
(dehydrogenation reactions) can be reduced by
cessing lighter crudes with higher costs that raise
dosage of antimony compounds that act like neu-
the operational costs and reduces the flexibility of
tralizing agent of the nickel dehydrogenation activi-
the refiner in relation of the crude oil supplier.
ty, reducing the generation of low added value gas-
es, in its turn, the vanadium effects can be con- The other steps of the residue fluid catalytic
trolled through the addition of rare earth to the cracking (RFCC) are essentially the same to the
catalyst, like cerium compounds. The addition of conventional fluid catalytic cracking (FCC), Figure
these compounds needs to be deeply studied once 3 shows a process scheme for a typical gases re-
raises significantly the catalyst cost. covery section of fluid catalytic cracking units.
The use of visbreaking units to treat the feed Some of the most relevant residue fluid catalytic
streams to RFCC units is a process scheme adopt- cracking technologies available commercially are
ed by some refiners, in these cases, the most signif- the R2R™ by Axens Company, the INDMAX™
icant effect in the reduction in the residual carbon, process licensed by McDermott company and the
however, due to his higher effectiveness, the ten- RxPro™ process developed by the UOP Compa-
dency in the last decades is to treat the bottom ny.
barrels streams in deep hydrotreating or hy-
Due to the current tendency of reduction in the
drocracking units before to pump for RFCC units,
transportation fuel consumption, especially by the
with this processing scheme it’s possible to achieve
developed countries, the fluid catalytic cracking
lower contaminants content, mainly metals, leading
units (FCC) and residue catalytic cracking (RFCC)
to a higher catalyst lifecycle. Furthermore, the hy-
have been optimized to maximize the yields of
droprocessing has the advantage of the reduction
petrochemical intermediates, mainly propylene,
of the sulfur content in the unit intermediate
against the transportation fuels intermediates
streams, minimizing the necessity or severity of
(naphtha and LCO). Figure 4 shows a block dia-
posterior treatments, a clear disadvantage of this
gram to the PetroFCC™ technology developed
refining scheme is the high hydrogen consumption
by UOP Company aiming to maximize the
that raises significantly the operational costs.

Figure 3 – Process Flow Diagram for a Typical Gases Separation Section of Fluid Catalytic
Cracking Units (FCC/RFCC)
 PAGE 18

petrochemical intermediates production, other References

available technologies are the HS-FCC™ process
MYERS, R.A. Handbook of Petroleum Refining
developed by Axens Company and the Maxofin™
Processes. 3a ed. McGraw-Hill, 2004.
technology by KBR Company.
SPEIGHT, J.G. Heavy and Extra-Heavy Oil Up-
The fluid catalytic cracking units have a key role in
grading Technologies. 1st ed. Elsevier Press, 2013.
the current scenario of the downstream industry,
once allow a closer integration between refining ROBINSON, P.R.; HSU, C.S. Handbook of Petro-
and petrochemical processes in view of the afore- leum Technology. 1st ed. Springer, 2017.
mentioned tendency of reduction in the transpor- About the Author
tation fuels demand, making that the petrochemical
sector be responsible to sustain the crude oil de-
mand in the next decades.
Conclusion
Beyond the tendency of reduction in transporta-
tion fuels demand, the necessity to meet environ-
mental regulations like IMO 2020 requires a strong
reduction of contaminants content in residual
streams to produce commercial bunker. In the first
moment, there is a tendency of the bunker market
be partially supplied by diesel or bottom barrel Dr. Marcio Wagner da Silva is Process Engineer
streams with low sulfur content leading to a raising and Project Manager focusing on Crude Oil Refin-
in the diesel prices and a devaluation of the high ing Industry based in São José dos Campos, Brazil.
sulfur content fuel oil. This scenario can pressure Bachelor in Chemical Engineering from University
the refiners with low bottom barrel conversion of Maringa (UEM), Brazil and PhD. in Chemical
capacity to carry out capital investments to im- Engineering from University of Campinas
prove the production of high added value deriva- (UNICAMP), Brazil. Has extensive experience in
tives. In this sense, the residue fluid catalytic crack- research, design and construction to oil and gas
ing technologies (RFCC) can be attractive alterna- industry including developing and coordinating
tives, once allow a better balance between the flex- projects to operational improvements and debot-
ibility in relation of the quality of processed crude tlenecking to bottom barrel units, moreover Dr.
oil (heavier and cheaper crude oils), high yields of Marcio Wagner have MBA in Project Management
petrochemical intermediates and production of low from Federal University of Rio de Janeiro (UFRJ)
contaminants content derivatives which contributes and is certified in Business from Getulio Vargas
to enhance the refining margin. Foundation (FGV).

Figure 4 – PetroFCC™ Process Technology by UOP Company.