Hydrocarbon Processing - June 2021 - 58

Catalysts
motes mixing of the water and gas in the cooler itself. FCC wash
water rates are typically in the range of 1 gal/min-2 gal/min of
water/1,000 bpd feed (0.034 m3
/m3 feed-0.068 m3/m3 feed) to
maintain an acceptable concentration of free cyanides in water.
The preferred scheme is to send water collected from the higher-pressure
drums directly to the sour water stripper, as sending
water back to the catalytic fractionator drum can set up an HCN
recycle in the gas due to flashing off at the lower drum pressure.
APS appears to react with the FeS scale to help form iron bi),
which is more resistant to complexing with HCN.
sulfide (FeS2
APS is typically added to the wash water to maintain a low excess
ppm level and to ensure that the water samples have an amber
color. If the FeS scale no longer provides protection due to high
cyanides and insufficient APS dosage, then Prussian blue deposits
(indicative of ferrocyanides) are observed in the water samples.
Filming inhibitors minimize the impact of corrosion by providing
a thin barrier on surface equipment and reducing the
formation of H° atoms through the use of specially designed
filming inhibitor chemistries. The filming inhibitor must effectively
cover all equipment surfaces by using efficient dispersion
systems as for water washing and APS.
Many FCCUs have no history of cyanide-related problems.
However, closer monitoring may be warranted if significant
changes in feed quality (e.g., higher concarbon/N and/or operating
conditions) are observed. Several options for monitoring the
likelihood of wet H2
S damage occurring can be considered. Water
can be analyzed for total and free cyanides in water and the water
color can be checked, as a Prussian blue color would indicate
that the HCN has removed some FeS scale. Routine onstream
15
13
11
9
2.5
All
100
75
50
25
9
All
11
13
Catalyst circulation rate, T/min
CN control
FIG. 6. Regenerator operating parameters.
58 JUNE 2021 | HydrocarbonProcessing.com
Other supplier
15
All
3.5
4.5
Feed concarbon, wt%
CN control
5.5
Other supplier
All
100
75
50
25
4
5
6
Flue gas CO, %
CN control
7
Other supplier
8
ultrasonic thickness measurement (UTM) from the outside of
susceptible equipment can be performed, and H2
can be used to detect an increase in H2
patch probes
Takeaway. A change to a low delta coke catalysta
flux through metal walls.
at Refiner A
demonstrated that FCC profitability can be improved by increasing
heavier feed processing while expanding the envelope of the
operating parameters, even if poorer feed quality gives rise to increased
cyanide production and potential risk of wet H2
S damage.
A combination of monitoring, cyanide corrosion control and adjustment
of operating parameters is available to mitigate the risk,
instead of giving up on improved economics, while unveiling the
potential for further FCC regenerator design optimizations.
NOTE
a BASF catalyst
STEFANO RIVA is BASF's Europe/Middle East/Africa (EMEA)
Technical Service Manager. He has 30 yr of experience in the
refining industry. After graduating in chemical engineering at the
Polytechnic University of Milan, he joined ExxonMobil, where he
served for 8 yr in the FCC area. In 2002 he joined BASF, where
he gained further FCC catalyst experience and now supports
customers with FCC optimization and troubleshooting.
STEVE CHALLIS is a UK-based consultant at Chalcat Consulting
Ltd. with more than 30 yr of FCC process experience, including
unit design, operations optimization, troubleshooting, incident
investigation, turnaround and startup support, and engineer/
operator training. Mr. Challis worked with ExxonMobil for more
than 20 yr as a process specialist. Since 2009, he has acted as
an independent FCC Process Consultant. Mr. Challis graduated from the Imperial
College of London with an MSc degree in advanced chemical engineering.
100
75
50
25
685
705
725
745
Regenerator bed temperature, °C
CN control
Other supplier
765
Total CN, mg/l
Catalyst circulation rate, T/min
Total CN, mg/l
Total CN, mg/l
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