Overview of Gas Treatment: Natural Gas Treatment

Natural Gases from reservoirs can not be used in its raw form as it contain various contaminants. So natural gas must be treated before commercializing it and the process is known as gas treatment or natural gas treatment.

Contaminants of Natural Gas

Gas contains various contaminants

  • Ammonia (NH3)
  • Hydrogen Sulfide (H2S)
  • Hydrogen Cyanide (HCN)
  • Carbon Dioxide (CO2)
  • Carbon Sulfide (COS)
  • Carbon Disulfide (CS2)
  • Mercaptans (R-SH)
  • Water (H2O)
  • Sulfur Dioxide (SO2)

Gas contains other components and Heavy Hydrocarbons such as

  • Pentane
  • Hexane
  • Benzene
  • Toulene
  • Xylene, etc

Process Overview of Gas Treatment

Hydrocarbons in production wells constitute three parts; Oil, Gas, and Water (Fig. 1). In a three-phase separator, all three elements are separated. The natural gas containing various contaminants is then subjected to gas treatment processes to sell or market it for the end-user.

Process Overview
Fig. 1: Process Overview

Reason for Natural Gas Treatment

Removal of the above-mentioned contaminants are required for reason of :

  • Corrosion Control
  • Toxicity
  • Gas product specifications
  • To prevent poisoning of catalyst in downstream facilities
  • Control of the overall heating value of the natural gas
  • To meet environmental requirements
  • To prevent freeze out at low temperatures
  • To prevent hydrate formation

CO2 & H2S are very common contaminants in Natural Gas System

Reason for CO2 removal from Natural Gas:

  • When combined with water forms Carbonic Acid which is corrosive
  • CO2 reduces the BTU value of the gas
  • If present in 2-3% gas is not saleable.

Reason for H2S removal in Gas Treating:

  • Extremely toxic gas
  • Highly corrosive

Reason for Mercaptants (R-SH) removal during Gas treatment:

  • It has smell
  • If comes in contact with bacteria (inside the final product storage) then released H2S
  • 2R-SH Bacteria R-SSR + H2S

Specification for Export Quality Natural Gas

The following table shows the permitted quantities of elements in natural gas for export purposes.

SpecificationUnitsMaximumMinimum
Gross Heating ValveBtu/scf1154940
Carbon DioxideMole %1
NitrogenMole %2
Hydrogen Sulphideppm vol5
Mercaptan Sulphur Contentppm vol5
Oxygenppm25
Moisture Contentlb/MMSCF10
Max Water Dew Point°C2(at delivery pressure)
Max. Hydrocarbon Dew Point°C-2(at delivery pressure)
Table 1: Elements in Export Quality Natural Gas

Typical Sales Gas Specifications

Fig. 2 below shows the specification for shale gas and Fig 3 shows the specification for LNG products.

Sales gas Specification
Fig. 2: Sales gas Specification
LNG product Specification
Fig. 3: LNG product Specification

Natural Gas Treatment Steps

Gas treatment is achieved in three steps

  1. Gas Sweetening (Removal of H2S, CO2, etc)
  2. Gas Dehydration (Removal of Water)
  3. Gas Dew Pointing (Removal of Heavy Hydrocarbons)

The following Figure (Fig. 4) shows the steps involved in gas treatment process.

Gas Treating
Fig. 4: Gas Treating

Gas Sweetening Process

Various processes are used for Gas sweetening as listed below

  • Chemical Solvent
  • Physical Solvent
  • Chemical + Physical Solvent
  • Solid Bed
  • Direct Conversion

Acid Gas Removal Processes:

Chemical SolventPhysical SolventDirect Conversion
MEA (Mono Ethanol Amine)Selexol®Iron Sponge
DEA (Di-ethanol Amine)RectisolStretford
TEA (Tri-ethanol Amine)PurisolUnisulf
MDEA (Methyl Diethanol Amine)SpasolvTakahax
DIPA/Shell ADIP®Propylene CarbonateLO-CAT®
DGA/Fluor Econamine®EstasolvenLacy-Keller
Proprietary AmineAlkazidTownsend
Benfield (Hot Carbonate) Sulfint
Catacarb (Hot Carbonate)  
Giammarco-Vetrocoke (Hot Carbonate)  
Diamox  
Dravo/Still  
Table 2: Acid Gas removal Process

Gases removed by different processes:

ProcessGases Removed
 CO2H2SRHSCOSCS2
SOLID BED
Iron Sponge X   
SulfaTreat X   
Zinc Oxide X   
Molecular SievesXXXXX
CHEMICAL SOLVENTS
MEA – mono ethanol amineXX X*X
DEA – diethanol amineXX XX
MDEA – methyl diethanol amine X   
DGA – diglycol amineXX XX
DIPA – di isopropanol amineXX X 
Hot Potassium CarbonateXX XX
Proprietary Carbonate Systems     
Table. 3: Gases removed by different process

Process Capabilities for Gas Treatment

 Normally Capable of Meeting 1/4 Grain H2SRemoves Mercaptans and COS SulfurSelective H2S RemovalSolution Degraded (By)
MonoethanolamineYesPartialNoYes (COS, CO2, CS2)
DiethanolamineYesPartialNoSome (COS, CO2, CS2)
DiglycolamineYesPartialNoYes (COS, CO2, CS2)
MethyldiethanolamineYesSlightYesNo
Sulfinol®YesYesYesSome (CO2, CS2)
Selexol®YesSlightYesNo
Hot Pot – BenfieldYesNoNoNo
Fluor SolventNoNoNoNo
Iron SpongeYesPartialYes––
Mol SieveYesYesYes––
StretfordYesNoYesCO2 at high concentrations
LO-CAT®YesNoYesCO2 at high concentrations
ChemsweetYesPartial for COSYesNo
Table 4: Process Capabilities of Gas Treatment
Gas Sweetening
Fig. 5: Gas Sweetening

Gas Dehydration

  • Glycol Dehydration
  • Solid Desiccant Dehydration
Gas Dehydration
Fig. 6: Gas Dehydration

Gas Dew Pointing for Gas Treatment

The gas dew pointing is done in any of the gas treatment methods mentioned below:

  • Propane Refrigeration
  • J-T Refrigeration
  • Turbo Expander

Fig. 7 shows typical schematic of Refrigerated J T Process

Refrigerated J T Process
Fig. 7: Refrigerated J T Process
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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

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