Hydrocarbon Processing - April 2022 - 15

Special Focus Maintenance and Reliability
S. COPPER and B. VICERAL, Phillips 66, San Francisco,
California; K. THOMAS and S. GOFF, Phillips 66, New Orleans,
Louisiana; J. CONTRERAS and L. NYADONG, Phillips 66,
Bartlesville, Oklahoma; J. STAVROS, Phillips 66, Houston,
Texas; and N. HATCHER, Optimized Gas Treating, Austin, Texas
Investigation and diagnosis of startup
foaming issues at a new tail gas treater
In May 2021, Phillips 66 started up a
new methyl diethanolamine (MDEA)based
tail gas unit at its Belle Chasse,
Louisiana, refinery. Shortly after startup,
foaming in the amine regenerator forced
the unit to shut down. Amine manufacturers
had declared force majeure after the
February 2021 cold snap in Texas, so the
refinery was forced to find alternative solutions
to changing out the amine. This
article will discuss interpretations of ion
chromatography (IC), along with comprehensive
two-dimensional gas chromatography-mass
spectrometry results that
pertain to the root cause of foaming. Also
discussed will be acceptable regenerator
steam and reflux accumulator purge
rates, the appropriate antifoam injection
locations, the use of carbon beds for contaminant
removal, and the utilization of
carbon beds to remove submicron iron
sulfide particles, as well as tray ratings,
equipment design details and sulfur recovery
unit (SRU) operation.
Background. Prior to 2021, the Belle
Chasse refinery operated with two parallel
Claus SRUs that sent tail gas to a
single MDEA-based tail gas unit. The
refinery could divert SRU tail gas from
either SRU to a single forced draft incinerator
during startups, shutdowns and
emergencies. The refinery needed a new
tail gas treating unit (TGTU) to provide
redundant TGT capacity for the refinery,
thus allowing the refinery to continue to
operate and comply with New Source
Performance Standards (NSPS) Subpart
J requirements while the existing TGTU
was undergoing turnaround maintenance
and was consequently out of service.
New TGTU design-Process flow diagram.
The new TGTU was designed to
handle Claus tail gas from two SRUs that
have an operating capacity of roughly
50-long-tpd and 75-long-tpd sulfur, respectively.
A new natural draft incinerator
was provided to complement the existing
incinerator.
Claus plant tail gas from either SRU
can be sent to the new TGTU. The Claus
plant tail gas is first heated by a 600-psig
steam heater to attain adequate reaction
temperatures for the cobalt molybdenum
(CoMo) catalyst to convert sulfur species
to hydrogen sulfide (H2
S) (FIG. 1).
The hydrogen necessary for the reactions
in the CoMo catalyst bed to proceed is
supplied by reformer hydrogen. There is
no waste heat boiler downstream of the
CoMo catalyst bed. The new TGTU was
originally designed with a spray cooler
on the quench column inlet piping, but
the spray cooler was never installed. The
quench water heat exchangers, which use
cooling water, provide all the cooling for
the quench column. The quench column
has a single bed of random packing. The
circulating quench water has a filter designed
for 25% of the normal quench
water flow. Quench water pH is continuously
monitored online upstream of the
quench water coolers. If the quench water
pH drops, caustic [sodium hydroxide
(NaOH)] is added automatically to increase
the pH of the quench water.
The MDEA section of the TGTU uses
generic MDEA. Designed MDEA circulation
is 130 gpm of 30 wt% MDEA solution.
The 4 ft-diameter MDEA absorber
is a column with two 12 ft-deep beds of
random packing and an overhead demister
(FIG. 2). Absorber overhead is sent
directly to the incinerator. A carbon bed
is provided on the rich amine leaving the
absorber. Particulate filters are provided
upstream of the carbon bed to prevent
FIG. 1. CoMo reactor and quench column.
Hydrocarbon Processing | APRIL 2022 15
Hydrocarbon Processing - April 2022

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