Hydrocarbon Processing - February 2022 - GP-18

SPECIAL FOCUS: TREATING SOLUTIONS
(~ 1 mol%), while the north section
of the field has more acid gas in the
cap gas (~ 2.3 mol%). This resulted
in a major discrepancy between the
actual feed gas composition and the
original composition that was used
during the design.
* The inlet gas temperature was
too high and resulted in lower
amine capacity and, consequently,
limited the AGRU from
accommodating higher feed gas.
* The current piperazine
concentration of 4 wt% contributed
to the limited amine capacity to
process additional acid gas.
* The upstream equipment was
inefficient in removing entrained
liquids. The inlet slug catchers did
not have internals to reduce liquid
carryover, and the inlet feed gas
filter separator size was inadequate
to handle the design flowrate
at actual conditions.
RECOMMENDATIONS
Install a dewpoint control unit (DPCU)
upstream of the AGRU. The DPCU will
eliminate the impact of fluctuating sour
feed gas conditions (liquid carryover, temperature
and composition). It will ensure
stable and lower feed temperature to the
AGRU, remove heavy hydrocarbons, significantly
improving the performance of
the AGRU and enable the unit to process
more sour gas. The design of the DPCU
considers multiple raw crude and gas cap
samples representing the field.
The raw data is used to develop a new
simulation of the plant based on the latest
crude oil and cap gas composition, representing
the north and south part of the field
to design the new DPCU and debottleneck
the current AGRU capacity limitation.
Although this option will imply capital
investment, it is the ultimate solution to
resolve the frequent foaming and limited
AGRU capacity. It is critical to consider
such an option at the early stage of plant
design, bearing in mind all factors that
affect the decision (i.e., actual gas hydrocarbon
dewpoint temperature, content of
C6
+, ambient conditions, length and size
of feed gas pipelines).
The new simulation results and actual
gas composition measurements will be
used as the basis for any new plant modification
and DPCU design (FIG. 4).
FIG. 4. Schematic of the proposed dewpoint control unit.
Increase piperazine concentration.
The increase of piperazine concentration
will result in higher capacity (pickup ratio)
and a lower contactor temperature in active
trays, which will further increase unit
processing capacity. In this case, the lower
design piperazine concentration provided
the flexibility to increase the concentration
to support higher amine loading.
This proposal was simulated using
process simulation softwarea
, and the new
temperature profile showed that acid gas
absorption is enhanced, which will allow
the amine contactor (FIG. 5) to accommodate
more acid gas content (a 4°F reduction
in bulge temperature was realized).
FIG. 5. Amine contactor temperature profile for GT#1.
18 JANUARY/FEBRUARY 2022 | GasProcessingNews.com
Modify the slug catcher internal. The
three slug catchers are the first protection
layer to remove the heavy hydrocarbon
from the associated gas fed via pipelines.
The existing slug catchers were provided
with conventional demister mesh pads,
which proved to be inefficient and resulted
in a significant amount of liquid
hydrocarbon and water carryover with the
gas stream to the amine unit. The situation
was aggravated under the several operating
scenarios, such as occasional slug flow
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Hydrocarbon Processing - February 2022

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