METHODS TO REMOVE CONTAMINANT


Methods to Remove Contaminant in Natural Gas Dehydration Process

The common natural gas contaminant are
  1. Water
  2. Hydrogen Sulphide
  3. Inert Gases
1. Methods to Remove Water
We remove most of the water with separator at gas head but water vapors in the gas stream are not removed.
These vapors causes hydrate formation; hydrates are combination of hydrocarbons molecules and water.        
Disadvantages of Hydrate Formation
Following are the disadvantages of hydrate formation.
  • That form solid and deposit themselves on pipeline interior, restricting the flow of gas. 
  • Water can also be contribute to corrosion in pipeline.
Dehydration
The process of removing water from substances is called dehydration.  

Most common method for dehydrating a natural gas stream.
  • Liquid desiccator or drying agent called glycol.
  • Solid bed desiccant ( Molecular sieve)
  • Methanol Injection

  • Liquid desiccator or drying agent called glycol.

During this dehydration process glycol absorbs water from gas stream, drying the gas, the glycol in-fact acts as a kind of sponge socking the water out of gas stream. The most glycol dehydration methods use tri-ethylene glycol contactor column or ethylene glycol injection system. At Nandpur gas field tri-ethylene glycol contactor column method is consider. 

I am not going in details for these methods, which i am not experiencing in the field.

  • Solid bed desiccant ( Molecular sieve)
  • Methanol Injection

2. Methods to remove Hydrogen Sulphide
Hydrogen sulphide which is also known as by its chemical symbol H2S. Hydrogen sulphide is an acid gas and an acid gas is gas which is forms acid when combine with water.

Acid Gases
Two examples of acid gas are hydrogen sulphide and carbon dioxide.

Nature of Hydrogen Sulphide
  • Hydrogen sulphide is corrosive and highly toxic gas.
  • It can be deadly, if proper safety procedures are not following in hydrogen sulphide case.  

They are several methods to remove hydrogen sulphide.

  • Chemical reactions

Ø  Amine sweeting

  • Membrane separation
  • Batch process

Ø  Iron sponge
Ø  Zinc oxide
Ø  Molecular sieves
Ø  Caustic wash


3. Methods to remove Inert Gases
Most common of these gases are carbon dioxide and nitrogen. These and any other noncombustible gases must be removed from the gas stream because it cannot burn and have no heating value. Method varies depend on type of gas being removed. 

  • Caustic waste in the amine process is usually removed carbon dioxide the same way they do hydrogen sulphide.
  • Nitrogen removed by Nitrogen Rejection Unit (NRU).

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