Simulation results from MEA and piperazine (PZ) activated MDEA (aMDEA)
Parameter
MEA
MDEA/PZ
MDEA/PZ
MDEA/MEA
MDEA
MDEA/PZ (optimised)
Inlet CO₂, mol% Inlet H₂S, ppm
1.55 150
1.55 150
1.55 150
1.55 150
1.55 150
1.55 150
Gas flow, MMSCFD
11 75 83
11 75 83
11 75 83
11 75 83
11 75 83
11 75 83
Inlet gas temperature, ºF
Pressure, PSIG
Inlet amine temperature, ºF Fixed L/R exchanger, mol/mol
110 yes 54.0 15.0
110 yes 45.0 30.0
110 yes 54.0 48.0
110 yes
110 yes 54.0 50.0
110 yes
Amine flow, GPM
54.00
45
Amine concentration, wt% Activator concentration, wt% Rich loading, mol/mol Lean loading, mol/mol Overhead temperature, ºF
48.0
48.0
0.0
2.0
2.0
2.0
0.0
2.0
0.356 0.085 229.0
0.200
0.103 0.004 227.0
0.100 0.005 225.0
0.026 0.003 238.0 1.307
0.111 0.005 215.0 0.658 1.218
0.0080
227.0
Outlet CO₂, mol% Outlet H₂S, ppm
0.0012
0.5270 0.6510 20,224
0.5590 0.6233 19,789
0.5760 0.9921 19,544
0.08
4.14
Heat exchanger duty, W/K Reboiler duty, BTU/Gal
19,015
20,836
17,220
1,023
791
698
698
559
632
Table 1
within guidelines, the unit should increase the amine sol- vent circulation rate for example. However, because of reboiler limitations, the regeneration capacity was at a maximum for the current solvent flow rates. Any increase in recirculation rates would require an increase in reboiler duty that was not available (a 25% increase in recircula- tion rates translates to an increase of 25% in reboiler duty). Alternative options to lower the rich amine loading was to use higher solvent strength. However, a 20 wt% maximum MEA concentration is recommended to minimise the sol - vent intrinsic corrosivity. The amine unit needs to target a regenerator overhead temperature of at least 215°F, or corrosion in the hot lean sections of the unit will continue to occur Based on a review of amine unit operation and simulation, it was apparent that rich amine solvent regeneration could be occurring too low in the regenerator tower and possibly into the reboiler. The prime reason for this is a low rich amine approach temperature to the regenerator (rich outlet temper- ature from the lean/rich (L/R) exchanger). The L/R exchanger should attain a minimum 195°F rich amine outlet temper- ature. According to operational parameters, the rich amine approach temperature to the regenerator is only 160°F. This means the steam must heat the amine solvent by nearly 90°F instead of the typical 45-55°F. The extra steam wasted in heating the solvent reduces the amount of steam available to strip the CO₂ and H₂S from the rich amine sol - vent. This means the regenerator tower basically runs out of
steam before it reaches the top section, so rather than strip- ping CO₂ and H₂S out in the top of the tower (ideal situa - tion), the acid gas travels deeper down into the regenerator section and even enters the reboiler before the regenera- tion takes place. This is one of the most common causes of regenerator corrosion and higher suspended solids in the lean amine solvent (compared to the rich amine solvent). In fact, a maximun of 5% rich amine should enter the reboider section to minimise corrosion (95% of the CO 2 is removed prior to entering the reboiler). The amine unit needs to target a regenerator overhead temperature of at least 215°F, or corrosion in the hot lean sections of the unit will continue to occur. The elevated stainless corrosion in the unit is not a normal occurrence when signs of carbon steel corrosion are low. High chloride levels in the solvent are most likely contributing to corro- sion of the stainless steel sections, along with the elevated acid gas content of the amine solvent. The most common mechanism of chloride ingression to the amine unit is with the feed gas, dissolved in the liquid water that enters the process. Liquid water should be removed prior to the amine unit using properly designed and operated slug catchers and high-efficiency cartridge-style gas coalescer systems. However, experience shows that most gas processing units lack efficient feed gas solid and liquid contaminant removal devices. This contaminant ingression with feed gas is also the primary reason for amine solvent foaming. Solids and/or water slugs, pipeline foam, back power, aerosolised liquid, and vessel deficiencies (design and operation/maintenance) can all lead to ingression of contaminants into the amine units. Liquid water entrained in the feed gas usually con- tains high levels of salt, generally sodium chlorides, with some smaller proportions of potassium, calcium, and mag- nesium components.
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PTQ Q4 2025
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