Hydrocarbon Processing - April 2022 - 19

Maintenance and Reliability
was effective in this case. Unfortunately,
the unit was not built with antifoam injection
facilities that would allow antifoam
injection directly into the amine
regenerator where the foaming problems
were manifesting. The only as-built antifoam
injection point was directed into
the amine absorber, a packed column
where foam is less likely to occur than
in the trayed regenerator. Any antifoam
injected into the absorber would have to
pass through the activated carbon beds,
where it would be adsorbed before getting
into the trayed regenerator. Consequently,
the refinery had to build a new
antifoam injection facility that allowed
antifoam injection into the regenerator
reflux piping. The antifoam was effective
when used at this location.
The unit engineer contacted the carbon
vendor and verified that the activated
charcoal used in the unitb
will adsorb
polypropylene glycol antifoam. Simple
shake tests indicated that the amine was
foaming more on the outlet of the activated
carbon bed than on the inlet of
the carbon bed, which indicated that the
carbon bed was completely spent at times
and needed to be changed out. It is also
possible that the activated carbon was
removing the antifoam and preventing
its access to the regenerator. The unit engineers
changed out the activated carbon
to a fresh bed prior to the next startup.
TABLE 1. IC analysis of the amine sample
Ions, μg/mL
593-102 TGT
lean MDEA
Sodium
Ammonium
2-methylaminoethanol
MDEA
Diethanolamine
Chloride
Nitrate
Phosphate
Sulfate
Sulfite
Thiocyanate
Thiosulfate
Acetate
Formate
Sulfide
Carbonate
1.6
5.6
586.9
130,539.7
1,685.1
31.7
< 0.1
< 0.1
894.6
535.6
< 0.1
1,503.4
< 0.1
76.9
4,107.7
1,715.2
FIG. 9. A graphical representation of the results of a comprehensive two-dimensional gas
chromatography-mass spectrometry analysis of the refinery tail gas amine.
Hydrocarbon Processing | APRIL 2022 19
FIG. 8. Foaming propensity test.
Ion chromatography. IC results from a
sample of lean TGT amine are shown in
TABLE 1. Thiosulfate, sulfite and sulfate are
present at noticeable levels. These data
were initially interpreted as the results of
an SO2
the green amine, since SO2
breakthrough, which could explain
is corrosive
in amine. However, the sulfide content
was very high for tail gas MDEA (4,107
ppmw). High sulfide content means that
the lean H2
S loading of the sample is
high. This sulfide content or lean loading
is so high that it would explain any stack
emissions issues encountered at this unit.
When lean (or rich) amine loading is high,
thiosulfates, sulfites and sulfates are very
likely to be generated by oxygen in the
sample bottles contacting the amine solution
and reacting with the sulfides. Based
on this IC result, there was no reason to
focus on SO2
breakthroughs. The focus
was put on amine regenerator operation
to reduce the lean loading of the amine.
It is most plausible that much of the color
and iron sulfide in the amine resulted
from inadequate regeneration, leading
to high HS-
concentrations in the amine
contacting the hot section of the amine
plant that has carbon-steel components.
Another reason to strip the amine adequately
in the regenerator is to remove
heavy hydrocarbons that might accumulate
in the tail-gas amine. The source of
hydrogen in this refinery is reformer hydrogen
that can contain small amounts
of aromatic hydrocarbons. Maintaining
adequate tail gas regenerator overhead
temperatures [> 115.56°C (> 240°F)]
Hydrocarbon Processing - April 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - April 2022
