Jump to content







Photo * * * * - 1 votes

Frequently Asked Questions (Faq) About Liquefied Natural Gas (Lng)




Frequently Asked Questions (Faq) About Liquefied Natural Gas (Lng) Dear All,
 
LNG is a subject of great interest these days considering that it has become a primary source of energy for many countries deficient in fossil fuel based energy resources. It is also of interest because it is among the cleanest of all fossil fuel based energy resources when compared with other fossil fuel energy sources such as coal and crude petroleum and its derivatives. 
 
Today's blog entry tries to put in perspective what LNG is all about. The focus is on introducing what LNG is to new engineers starting their career. The blog entry has been made in the form of 'frequently asked questions' related to LNG. Details are excluded and certain web references are provided as hyper links which can guide the readers where to look for more details. Here goes the FAQ:
 
Q1. What is LNG?
A1. Liquefied Natural Gas (LNG) is natural gas (NG) that is cooled to the point that it condenses to a liquid.
 
Q2. What are the conditions for natural gas to be converted to LNG?
A2. Natural gas condenses to a liquid i.e. becomes LNG at a temperature of approximately -161°C (-256°F) at atmospheric pressure (101.325 kPaa).
 
Q3. Why is it required to convert natural gas to LNG?
A3. Liquefaction of natural gas to LNG reduces the volume of natural gas by approximately 600 times thus making it more economical to store natural gas and to transport gas over long distances for which pipelines are not economically feasible or there are other constraints.
 
Q4. How is LNG stored?
A4. LNG is stored in double-walled storage tanks at atmospheric pressure. The storage tank is really a tank within a tank. The annular space between the two tank walls is filled with insulation. Refer the link below for more information on LNG storage tanks:
http://en.wikipedia....NG_storage_tank
 
Q5. What materials are used to construct LNG storage tanks?
A5. The inner tank in contact with the LNG is made of materials suitable for cryogenic service and structural loading of LNG. These materials include 9 percent Nickel Steel, aluminum and pre-stressed concrete. The outer tank is generally made of carbon steel or pre-stressed concrete.
 
Q6. How is LNG transported by ships?
A6. LNG tankers are double-hulled ships specially designed to prevent leakage or rupture in an accident. The LNG is stored in a special containment system within the inner hull where it is kept at atmospheric pressure and cryogenic temperature (-161°C). For more details refer the following link:
http://en.wikipedia....iki/LNG_carrier
 
Q7. What is re-gasification of LNG?
A7. LNG has to be converted back to natural gas by warming in a controlled environment at the receiving and re-gasification terminal. The LNG can be warmed by passage through pipes heated by direct-fired heaters, or pipes warmed by seawater, or through pipes that are in heated water.
 
Q8. How is LNG quantified for trading (selling / buying) in the world market?
A8. LNG is generally quantified for trading on a mass basis in terms of millions of tons 
 
Q9. Is there an approximate conversion for LNG mass to NG volume at standard conditions of 1 atmosphere pressure and 60°F?
A9. The approximate conversion for LNG mass to NG volume at standard conditions of 1 atmosphere pressure (14.7 psia /101.3 kPaa) and 60°F is as follows:
 
1 Metric ton of LNG or 1000 kg of LNG = 48,700 Scf of NG = 1379 Sm3 of NG
 
Note: Exact conversion depends on natural gas molecular weight
 
Q10. Is LNG flammable?
A10. LNG when suddenly released from its containment to atmosphere at ambient temperature conditions flashes and forms a vapor-air mixture. This vapor-air mixture forms a visible vapor-air cloud. As the vapor cloud gets warmer in contact with the ambient air it gets lighter than air and rises. A flammable vapor-air mixture can only form if the natural gas vapor concentration in the vapor-air mixture is between 5% and 15% by volume of the vapor-air mixture. A vapor-air mixture with less than 5% by volume of NG cannot cause a flame or fire since the concentration of the vapor (NG) in the vapor-air mixture is not enough to start or sustain a flame or fire or in other words the vapor-air mixture is too lean. The value 5% by volume is thus called the Lower Flammability Limit (LFL) for natural gas. Similarly a vapor-air mixture with more than 15% by volume of NG cannot cause a flame or fire since the concentration of the air (oxygen) in the vapor-air mixture is not enough to start or sustain a flame or fire or in other words the vapor-air mixture is too rich. The value 15% by volume is thus called the Upper Flammability Limit (UFL) for natural gas.
 
Q11. Is LNG explosive?
A11. LNG in its liquid form is not explosive. When LNG forms a vapor-air mixture and is in a confined space with no means to disperse it can cause a vapor cloud explosion if exposed to a source of ignition. Again for the vapor-air mixture to explode, the vapor concentration of natural gas in the vapor-air mixture has to be between 5% and 15% by volume. Thus the term LFL / UFL is interchangeably used with the term Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).
 
Q12. What are the main uses of LNG?
A12. LNG after re-gasification to NG is primarily used for power generation, home heating and as cooking gas. 
 
For more details related to LNG in general refer to the links below:
http://www.beg.utexa...energyecon/lng/
http://en.wikipedia....ied_natural_gas
 
I have no claim whatsoever as an expert in the LNG field. This is a general information that has been provided in this blog. I will take questions from the readers and try to answer them to the best of my ability.
 
Happy reading.
 
Regards,
Ankur.
 
 
 




thanks Ankur

Thank you very much sir, its very useful.

Great Post

Thank you for the information, Sir

Thanks sir, really appreciate the info u have provided.

Thank you sir,  really its very useful.

Photo
pankajranga
Dec 12 2013 12:54 AM

Excellent post Aankur, for bigginer

useful thanks

Is NG C1, C2, C3, C4 or a mixture of the four gaseous alkanes? Are other (nonalkane) gases also recognised as NGs (e.g H2S?)?

Photo
ramlalithravi
Jun 26 2014 07:11 AM

What is difference between LNG (Liquified natural gas) and Natural Gasified liquid (NGL)?

 

If the natural gas is liquified by compression at high pressure, does it still call as LNG? pls clarrify

Is NG C1, C2, C3, C4 or a mixture of the four gaseous alkanes? Are other (nonalkane) gases also recognised as NGs (e.g H2S?)?

NG is predominantly C1 with other heavier hydrocarbons constituting the rest. NG classified as "Sour NG" contains significant amount of H2S.

 

Regards,

Ankur.

What is difference between LNG (Liquified natural gas) and Natural Gasified liquid (NGL)?

 

If the natural gas is liquified by compression at high pressure, does it still call as LNG? pls clarrify

NGL is an abbreviation for "Natural Gas Liquids". These are the heavier hydrocarbon constituents (C3+) found in NG and can be readily separated as  liquids by suitable modern procsses such as refrigeration and turbo-expansion.

 

LNG is "Liquefied Natural Gas" which is obtained by cooling natural gas. Only compression cannot be used to liquefy natural gas. Fundamentals for phase change of any gas require it to be cooled below it's critical temperature to obtain liquid. At or above the critical temperature no amount of increase in pressure will liquefy the gas.The minimum pressure required to liquefy the gas below the critical temperature is thus called the critical pressure.

 

Regards,

Ankur

Photo
yogeshdafade
Jun 30 2014 10:09 AM

Thanks Ankur.

Sir, Can you please provide some information about converting Natural gas to Gasoline and its future prospects.

Hi Everyone, I have worked in LNG since 1977.

I currently work (as a consultant) at an LNG import/regas terminal and have worked on LNG ships and LNG production. I have commissioned and decommissioned LNG plants and terminals.

I am happy to answer questions and share what I know.

Best wishes

Adrian

Latest Visitors

  • Photo
    seshadri
    Today, 04:17 AM
  • Photo
    12345656
    Today, 12:33 AM
  • Photo
    Bodhisatya
    Yesterday, 09:50 AM
  • Photo
    iboras
    Yesterday, 07:15 AM
  • Photo
    nalawade_pradeep
    Yesterday, 06:16 AM
  • Photo
    Said Salim
    Yesterday, 04:33 AM
  • Photo
    clarenceyue
    Yesterday, 03:33 AM
  • Photo
    gdnicoll
    21 Nov 2017 - 21:27
  • Photo
    kehugyhl
    21 Nov 2017 - 18:13