Hydrocarbon Processing - October 2022 - 20

Plant Safety and Environment
plate heat exchanger to 40°C (104°F)
with chilled EG. The cooled solvent was
pumped to the absorber. The chilling loop
system of a chilled water loop, filled with
EG (30 wt%), was cooled to 10°C (50°F)
with a chiller unit. The total circulation
rate of chilled water was 4 m3
/hr, with a total
process flow requirement of 0.4 m3/hr.
The unit was fitted with an online gas
chromatograph (GC) for gas analysis. Of
this setup, three gas streams were analyzed
online: the outlet of the compressor, the
outlet of the absorber and the outlet of the
stripper. The analysis of the liquid amine
solvent was done offline in the Dow
Industrial Solutions lab in Terneuzen,
Netherlands. The process GC system
Results and discussion. The operational
period for the pilot line started with
commissioning in 2H 2018. Operations
commenced in 2019 and continued in
2020-2021. Over time, the unit availability
increased, enabling extended campaigns
lasting multiple months at a time. The run
length was initially limited by excessive
pressure drop over the inlet filters. Improvements
to the filter design enabled exwas
equipped with five parallel chromatographic
trains to separate all major components
with a cycle time of 300 sec.
To deliver on the research objectives,
the pilot line was operated continuously
for specific periods of time in 2018-2021.
tended run lengths between filter changes.
The data presented here are mostly
from 2020 and comprise two periods:
* Experiment 1 (Exp. 1), in which the
unit was operated for ~800 hr on
BFG only (blue data points), BFG +
COG mix (purple datapoints) and
COG only (red datapoints)
* Experiment 2 (Exp. 2), in which
the unit operated for ~2,500 hr
on BFG only.
In total, the unit captured ~2.2 t of CO2
during Exp. 1 and 9.2 t of CO2
during Exp.
2, based on mass balancing with the mass
flowmeters and gas composition data
from the online GC. In Exp. 1, the cleaned
gases from the absorber were routed to
a downstream unit of LanzaTech, which
utilized the treated gas as a feedstock for
ethanol production (not reported here).
The CO2
Exp. 1 and Exp. 2 are presented in FIG. 5.
The data shows that the targeted CO2
removal
efficiency of 90%-95% could be
achieved for extended periods of time.
During Exp. 1, process conditions were
optimized-namely solvent circulation
rates and energy input-to reach CO2
removal
efficiencies of 95%-100%, albeit at
an increased heating duty in the reboiler.
It was found that performing a detailed
FIG. 5. CO2 removal efficiencies during Exp. 1 and Exp. 2. In these periods, a total of 2.4 t and
9 t of CO2
were captured, respectively. Exp. 1 was BFG only (blue data points), BFG + COG
(purple data points) and COG only (red data points). Exp. 2 (black data points) was BFG only.
energy balance of the system to evaluate
energy input per unit mass of CO2
removed was not possible on the pilot
unit. Primarily due to the high relative
heat losses at this smaller scale at various
locations in the process, it was found that
the measured number had a high standard
deviation from the actual number. Dow
Industrial Solutions supports hundreds of
commercial CO2
capture units, and it has
a proprietary empirical model that predicts
the performance of such units. For
this small-scale pilot, the heating duty was
calculated to be 4.2 GJ/mT of CO2
captured
in an idealized configuration. However,
the model predicts that this would
translate to 2.3 GJ/mT of CO2
in a commercial-scale installation. This is
well in line with world-class performance
for an amine-based CO2
capture unit.12
The impurities present in COG can
FIG. 6. Concentration of HSAS as a measure of solvent quality for Exp. 1 (black data points) and
Exp. 2 (blue, purple and red data points) as a function of time.
20 OCTOBER 2022 | HydrocarbonProcessing.com
lead to foaming, fouling and a higher buildup
of heat-stable amine salts (HSAS),
which can have a significant negative impact
on the performance of the system.
HSAS are the amine salts of acidic contaminants
that do not thermally split and
liberate in the regenerator. In the chemical
captured
removal efficiencies during

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Hydrocarbon Processing - October 2022

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