Hydrocarbon Processing - April 2022 - 17

Maintenance and Reliability
Foaming diagnosis. The TGTU amine
regenerator performance during 1 hr
in June 2021 is illustrated in FIGS. 3 and
4. The stripper bottom level and reflux
drum level shown in FIG. 3 are stable until
the stripper tray pressure drop starts rising
quickly at approximately 7:45 p.m. Minutes
later, the stripper bottom level drops
quickly, followed by the reflux drum level
quickly rising to 100%. FIG. 4 shows that
acid gas recycle initially drops when the
stripper pressure drop starts rising, and
then goes off scale high when all the liquid
holdup in the column is pushed overhead
into the reflux accumulator. The behavior
shown in FIGS. 3 and 4 is consistent with
foam starting first in the stripping section
of the regenerator, with amine unable to
reach the bottom of the regenerator and
then " burping " into the reflux accumulator.
FIG. 4 also indicates reflux flowback
to the stripper going off scale high as the
operations team attempted to reduce the
reflux accumulator level. FIG. 4 shows that
steam had to be cut to lower the stripper
pressure drop and to avoid a reflux accumulator
overfill. FIGS. 3 and 4 indicate
classic foaming behavior, with foaming
far worse in the trayed amine regenerator
than in the packed amine absorber.
The TGTU MDEA absorber's ∆P and
level control were not affected as significantly
during the same time interval. The
TGTU absorber bottoms level was maintained
in the 45%-52% range, and the
TGTU absorber ∆P stayed within a tight
range of 0.35 psi-0.71 psi. Similar behavior
repeated itself during similar time periods
for the next few weeks.
SRU troubleshooting. The larger
75-long-tpd SRU had plugging concerns
during the startup of the new TGTU. Sulfur
carryover from the final condenser
into the TGTU catalyst bed was also hypothesized.
It was initially thought that
these issues might be related to TGTU
foaming, and troubleshooting efforts began
to resolve these issues.
The largest pressure drop in the SRU
was measured across the first converter
catalyst bed. Heat transfer in the first converter
bed reheater was also severely limited,
resulting in poor SRU conversion
during the new TGTU startup. During
this time, a low outlet temperature from
the first sulfur condenser was evident.
The plugging could be temporarily alleviated
by unplugging the seal leg, leaving
the first condenser. When the first
seal leg started flowing liquid sulfur, the
performance of the first reheater gradually
improved as sulfur melted away from
the first reheater. As the reheater performance
improved, the temperature of the
first catalyst bed started rising, improving
overall sulfur plant conversion.
At this time, the refinery hypothesized
that there was a water leak in the
first condenser that was plugging the
sulfur rundown leg and allowing sulfur
to accumulate and then get entrained
and carried into the first reheater where
the sulfur stuck onto cold parts of the
reheater. There were also some thoughts
that the carryover was due to poor heat
transfer from the steam tracing on the
aboveground sulfur seal legs. To prove
conclusively that there was a water leak
from the condenser and not from the
upstream waste heat boiler, the refinery
decided to conduct radioactive tracer
testing on the upstream waste heat boiler
and the first condenser.
Radioactive tracer was injected into
the boiler feed water that supplied the
waste heat boiler and first condenser.
Tracer was injected on separate days into
the boiler and condenser. Tracer levels
were measured in the TGTU's quench
water on each day. Radioactive tracer tests
showed conclusively that the first condenser
was leaking-and that there was
no leak in the waste heat boiler. Maintenance
efforts could be concentrated on
fixing the first condenser.
Sulfur carryover from the final condenser
and TGTU catalyst activity.
Heat
transfer issues around the
final
seal leg in the larger 75-long-tpd sulfur
plant led to a decision to raise the final
condenser temperature to 290°F-300°F
(143.33°C-148.89°C) in June 2021.
Shortly after raising the temperature, refinery
personnel noticed that the top of
the TGTU hydrogenation catalyst bed activity
started dropping, while the middle
of the catalyst bed increased (FIG. 5). Total
catalyst activity-in terms of ∆T-remained
the same (FIG. 5).
Phillips 66 interpreted this catalyst
behavior as sulfur entrainment affecting
catalyst bed performance. Sulfur hydrogenation
is a slower reaction vs. other reactions
that occur in the tail gas catalyst bed,
and, consequently, the bulk of the tail gas
reactor exotherm has been shifted lower
in the bed. There was no change in emissions
associated with the changing ∆T in
the tail gas catalyst bed.
SRU troubleshooting efforts began
before laboratory results of the TGTU
amine analysis were obtained. While SRU
issues contributed to overall SRU/TGTU
performance, SRU issues were not the
root cause of the foaming issues.
Amine regenerator tray rating. Phillips
66 fractionation experts rated the
amine regenerator stripping trays at typical
operating rates prior to the foaming
events. Jet flood ranged from 41%-63%
as the system factor was varied from 1
FIG. 5. TGTU reactor zone's ∆T% and total ∆T (°F).
Hydrocarbon Processing | APRIL 2022 17
Hydrocarbon Processing - April 2022

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