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Natural Gas Sweetening
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Natural gas sweetening by Monoethanolamine process
Presented by:
Muhammad Ayaz Mazari (M08-PG 04)
Fazal Mehmood (M08-PG-18) Muhammad Waleed (M08-PG-07)
Contents
Natural gas sweeteningBackground Basic chemistrySelection criteriaMEA sweetening processProcess difficulties
Natural gas sweetening
Removal of unwanted and hazardous acid gases( CO2 and H2S) from raw natural gas is known as natural gas sweetening.
Methods commercially used for sweetening.Amine treatingBenfield processPSA processSelexol processSulfinol process
Background (Amine Treating)
1st ever alkanolamine developed was triethanolamine(TEA) by R. R. Bottoms in 1930.
Replacement of TEA by other aminesLow capacityLow reactivityRelatively poor stability
Background(Amine treating)
The relative development of different amines used in gas treating with the passage of time:
Monoethanolamine (MEA)
Diethanolamine (DEA)
Methyldiethanolamine (MDEA)
Diisopropylamine (DIPA)
Aminoethoxyethanol (diglycolamine) (DGA)
Background (Amine Treating)
The recent development in this context is Sterically hindered amines, which are replacing older amine technology…..
Basic chemistry
Principal reactions Ionization of water:
H2O = H+ + OH-
Ionization of dissolved H2S:
H2S = H+ + HS-
Hydrolysis and ionization of dissolved CO2:
CO2+ H2O = HCO3- + H+
Protonation of alkanolamine:
RNH2 + H+ = RNH3-
Carbamate formation:
RNH2 + CO2 = RNHCOO- + H+
Selection criteria of MEA
Following are the important factors for which MEA is used.
When raw gas contains low concentration of acid gases (H2S and CO2).
when minor contaminants such as COS and CS2 are present.
When raw gas is treated at low pressure.Due to its high alkalinity.Due to its easy reclamation from
contaminate.
Selection criteria of MEA
Following are the factors which forbid the use of MEA.
When raw gas contains high concentration of acid gases (H2S and CO2).
When raw gas is treated at high pressure.Irreversible reaction products with COS
and CS2 are formed when COS and CS2 are in excess
Selection criteria of MEA
More corrosive High heat of reaction with CO2 and H2S
which leads to high energy requirements for stripping.
Relatively high vapor pressure of MEA causes significant vaporization losses. particularly in low-pressure operations.
MEA Sweetening Process
Inlet gas knockoutAbsorberThree phase flash tankLean/rich amine heat exchangerRegeneratorFiltration
Inlet gas knockout
Raw natural gas is first subjected to inlet gas knockout drum
Entrained droplets and liquid are removedBaffles remove most of the liquid and mist
eliminator pads at the top remove the rest of it .
Absorber
Sour gas is introduced at the bottomLean amine solvent is introduced at the top.Either packed or tray columns may be used.Packing and trays are basically used to
increase contact time and area.Mist eliminators are installed at the top of
column.
Three phase flash tank
Rich amine from bottom is subjected to three phase flash tank
Which separates rich amine into three phases.
Lightest HC’s into gaseous, heavier HC’s and amine form two liquid layers.
Aqueous amine is freed from hydrocarbons.It controls amine solution and amine
sweetening system conditions.
Lean/rich amine exchanger
Rich amine is pre-heated before entering into the stripper.
This is done with lean amine coming from stripper bottom.
Usually shell and tube heat exchanger is usedThis reduces heat duty for reboiler.
Regenerator
Stripper is used for regeneration of amine.Stripper can be of tray type or packed
column.It works like a distillation column.
Filtration
Mechanical or activated column filtersFilters remove particulate solids, HC’s and
surface active compounds from amine.This reduces plugging and corrosion/erosion
rate.
Flow diagram
Process difficulties
Foaming Solvent lossesCorrosion Failure to meet gas specification
Thank you
