Natural gas sweetening

1
Natural gas sweetening by Monoethanolamine process
2

•  Presented by
• Muhammad Ayaz Mazari (M08-PG 04)
• Fazal Mehmood (M08-PG-18)
• Muhammad Waleed (M08-PG-07)

3
Contents

• Natural gas sweetening
• Background
• Basic chemistry
• Selection criteria
• MEA sweetening process
• Process difficulties

4
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 treating
• Benfield process
• PSA process
• Selexol process
• Sulfinol process

5
Background (Amine Treating)

• 1st ever alkanolamine developed was
  triethanolamine(TEA) by R. R. Bottoms in 1930.
• Replacement of TEA by other amines
• Low capacity
• Low reactivity
• Relatively poor stability

6
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)

7
Background (Amine Treating)

• The recent development in this context is
  Sterically hindered amines, which are replacing
  older amine technology..

8
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

9
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.

10
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

11
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.

12
MEA Sweetening Process

• Inlet gas knockout
• Absorber
• Three phase flash tank
• Lean/rich amine heat exchanger
• Regenerator
• Filtration

13
Inlet gas knockout

• Raw natural gas is first subjected to inlet gas
  knockout drum
• Entrained droplets and liquid are removed
• Baffles remove most of the liquid and mist
  eliminator pads at the top remove the rest of it
  .

14
Absorber

• Sour gas is introduced at the bottom
• Lean 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.

15
Three phase flash tank

• Rich amine from bottom is subjected to three
  phase flash tank
• Which separates rich amine into three phases.
• Lightest HCs into gaseous, heavier HCs and
  amine form two liquid layers.
• Aqueous amine is freed from hydrocarbons.
• It controls amine solution and amine sweetening
  system conditions.

16
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 used
• This reduces heat duty for reboiler.

17
Regenerator

• Stripper is used for regeneration of amine.
• Stripper can be of tray type or packed column.
• It works like a distillation column.

18
Filtration

• Mechanical or activated column filters
• Filters remove particulate solids, HCs and
  surface active compounds from amine.
• This reduces plugging and corrosion/erosion rate.

19
Flow diagram
20
Process difficulties

• Foaming
• Solvent losses
• Corrosion
• Failure to meet gas specification

21
Thank you