Hydrocarbon Processing - December 2022 - 47

Process Optimization
The adjustment of upstream cut-points
increased this further-the net result
is that the organic sulfur species in the
treated gas were reduced by 94% after
field optimizations.
At the end of the test run, SO2
emissions
associated with this absorber declined
by more than an order of magnitude.
Determining the source of the SO2
emissions and then optimizing process
conditions during a dedicated test run,
with testing and analytical support, significantly
decreased the already-low emissions
from the facility.
Takeaways. Field data reveal that generic
amines are capable of better organic
sulfur removal than historical literature or
commercial simulators now predict.
In one instance, DGA was able
achieve 100% removal of the COS, CH4
C2H6S and C3
S and C2
FIG. 10. Simulated vs. actual organic sulfur removal in a DEA fuel gas absorber.
to
S,
H8S, albeit at low gas-tosolvent
rates, which is not beneficial for
plant CAPEX and OPEX. Removal of
CH4
H6S by DGA correlated with
gas-to-solvent ratios, with lower ratios
showing higher rates of removal. Other
operating parameters investigated did not
appear to have a major impact for DGA.
DEA data shows a correlation between
COS and CH4
S removal and gas-to-solH6S
removal and lower
S and 60% C2
H6S was
vent ratio, as well as an unusual correlation
between C2
solvent strength. Removal of up to 100%
of COS, 80% CH4
observed on some systems.
Absorption of COS by MDEA appeared
to be linked to the temperature
bulge within the absorber, with 80% absorption
of COS by MDEA being the
maximum observed. MDEA showed
low absorption of methyl mercaptan
(20%-30%) with no obvious correlation
between the amount of absorption and
other process parameters.
For ethyl mercaptan removal, the data
showed an interesting trend of better removal
of ethyl mercaptan with declining
amine strength for MDEA and DEA,
which could potentially be explained by
a reaction mechanism in which the ethyl
mercaptan reacts with the water initially,
or viscosity effects.
For propyl, butyl and pentyl mercaptan,
removal in the range of 20%-80%
was observed in the field results, but
there were insufficient data to establish
links with process parameters or to draw
significant conclusions. The removal of
FIG. 11. Ethyl mercaptan removal in T2904 at Preemraff Lysekil.
DMS ranged from 22%-88%, with MEA/
DEA/MDEA capable of removing 70%
under certain process conditions.
In some instances, significant reductions
in organic sulfur in treated gas are
possible by optimizing process conditions.
This is best done through onsite analytical
testing, as both the fundamental
understanding of the behavior of organic
sulfur species and the simulation of this
behavior need improvement.
Further research is needed to improve
the industry's ability to predict (and
hence optimize) organic sulfur species
removal in amine systems. Specifically,
improvement in simulator prediction capabilities
is required. This will potentially
require the generation of new or better
experimental data for the solubility and
absorption of organic sulfur species in
amine systems on which simulator predictions
are based. Also of interest is the formation
chemistry of some organic sulfur
species in amine systems (e.g., mercaptan
formation from sour amine in the presence
of methanol) and potential routes
for DMDS formation.
ACKNOWLEDGEMENT
The authors would like to thank Preem AB for
granting permission to publish data from its Lysekil
facility.
NOTES
a Tedlar® bags
b Sulfinert® cylinders
d
c Agilent 6890 or 7890 gas chromatographs
Agilent GasPro columns
LITERATURE CITED
Complete literature cited available online at
www.HydrocarbonProcessing.com.
Hydrocarbon Processing | DECEMBER 2022 47
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