Hydrocarbon Processing - June 2022 - GP-29

PROCESS OPTIMIZATION
ened gas. The recovered amine is then
added with water in the mixer to reuse for
the new sweetening process cycle.
Simulation model. To model a realistic
gas sweetening process, a specified content
of CO2
that the sweetening agent's efficiency and
flow are modeled correctly. The normal
accepted content of CO2
natural gas should be 4 mol%-5 mol%.5
In addition, the content of CO2
when a gas
must be present. This ensures
in the untreated
in the
natural gas stream was 0.0049 mol%.
Therefore, water was added to the amine
solution. This is done to ensure a larger
surface of the liquid phase6
stream is added to an absorption column
with a relatively high flowrate, the corresponding
amount of amine will be relatively
low.7
If water is not added, it will be
impossible to ensure a good contact between
the gas and liquid, which will cause
a less-efficient sweetening process. Thus,
water is normally added up to 75 mol%
when performing gas sweetening.8
The absorption process takes place in a
column that contains a certain calculated
number of stages. The mass balance used
in this analysis was the McCabe-Thiele
model. The two inlet streams are the feed
gas and the lean amine. The temperature
of the amine-water stream should be at
least 5°C warmer than the acid gas stream
in the absorption column to avoid components
of the natural gas condensing into
the liquid amine stream. The pressure of
the absorption column during operation
was around 49 bar, which is normally accepted
for the absorption column.9
Results of steady-state simulation
and process optimization. To evaluate
the efficiency of gas sweetening, several
treatment cases were modeled in the
proprietary simulation softwarea
simulations, H2
. In all
S content had to be below
4 ppm to match the specifications for
clean gas. Nine cases were modeled to investigate
the efficiency of tray and packed
columns and to evaluate thermodynamic
models. The amine treatments used were
monoethanolamine (MEA), DEA, diglycolamine
(DGA), piperazine (PZ),
triethylamine (TEA), diisopropylamine
(DIPA) and MDEA. For all cases, the
amine packages (for acid gas cleaning) in
the modeling were used.10
Chemical absorption by amines.
Selecting the appropriate solvent for gas
Data of 4-F18
pressure 43 psi
temperature 180°F
flowrate 80 gpm
partial filtration
4-F19
2
4-F18
FIC-4008
4-E25
4-P48
Strainer
FIG. 1. Process flow diagram of the amine unit at the GUPCO plant.
Gas Processing & LNG | MAY/JUNE 2022 29
temperature 245°F
flowrate 220 gpm
1
Amine heater
4-H9
4-P47
4-T5
sweetening depends on various conditions
that can include the ability to remove
H2
S and CO2
, the pickup rate of
hydrocarbons, and the heat requirement
for solvent regeneration, as well as vapor
pressure, foaming, selectivity, thermal stability,
corrosivity, cost and availability.11
In this simulation experiment, amine and
amine blends were used as sweetening
solvent. The chemical reactions for MEA
and DGA included the following ( " R " refers
to amine):
* RNH2
+ H2S = RNH3
* RNH2 + H2O + CO2
* 2R2NH + CO2
HS
= RNH3HCO3
Chemical reactions for DEA are:
* R2NH + H2
S = R2NH2
HS
= R2NCOOR2NH2
+ H2S = R2NHCH3
+ CO2
R2NHCH3
HCO3
+ H2
.
O =
HS
.
Chemical reactions for MDEA and
DIPA are:
* R2NCH3
* R2NCH3
Process optimization. The aim of this
optimization work was to study the effects
.
of using various types of amine and amine
blends on amine plant performance.
Therefore, optimization options were
studied by applying various amines at constant
concentrations within the simulation
to monitor changes in the composition of
sour gas streams.
The experiments used 32 wt% of different
amine and amine blends in the GUPCO
gas sweetening plant by maintaining
some operational conditions (e.g, sour gas
stream pressure and temperature, and lean
amine pressure and temperature). Once
the simulation was concluded, the results
for H2
S and CO2
in the sweet gas streams
were recorded.
Parametric sensitivity analysis and
simulation modeling using MEA. In
TABLE 2, the H2
S composition of sweet
S from both the sweet
gas is 4.508e-004 ppm. The recovery
for removed H2
gas and the acid gas (H2
S and CO2) was
100%. Amine strength was 32 wt% and
the amount of regenerated steam required
PIC-4002
Treated gas to
pressure 80 psi
temperature 135°F
To acid flare
Skimmer 4-V38
LIC-4006
To flare
LIC-4007
4
4E-23
Temperature 180°F
To acid flare
Data of 4-F19
pressure 85 psi
temperature 190°F
flowrate 300 gpm
4-V3T
Temperature
247°F
PIC-4001
pressure 5 psi
4E-24
Temperature
130°F
LIC-4008
11
20
3
4-P46
Temperature
190°F
FIC-4009 300 gpm
temperature 140°F
LIC-4005
4-V3T
LIC-4004
4-T4
Sour gas
from 4-V15
4-V43 and 4-V143
14
Lean amine
Hydrocarbon Processing - June 2022

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