- Written by Eric Hahn
Natural Gas Liquids (NGLs) vs LPG vs LNG
Talk about alphabet soup…
NGL vs LNG vs LPG vs Natural Gas vs Condensate?
What are they, how are they used and what are the differences?
The typical LPG gases – propane and butane – are regarded as Natural Gas Liquids.
However, not all NGLs are LPG.
Natural gas liquids, also called Condensate, include other hydrocarbons, too.
Amazingly, LNG – liquefied natural gas – is NOT a natural gas liquid.
Seriously confusing, right?
It's confusing to me and I wrote it!
Well, let's try to fix that…
What are Natural Gas Liquids - NGLs?
Raw natural gas, as it comes out of the ground, contains a number of gases and compounds, as well as impurities.
However, it is predominantly methane (CH4) gas, which is more commonly known as natural gas.
The raw natural gas must be processed to obtain pipeline quality clean, dry natural gas (methane).
NGLs – Natural Gas Liquids – or condensate are the heavier hydrocarbons that remain after the methane (natural gas) is removed.
Natural Gas Liquids - NGL Terminolgy Chart
|Propane||LNG - Liquefied Natural Gas|
|Butane||CNG - Compressed Natural Gas|
What Compounds are Considered Natural Gas Liquids?
NGLs include propane, butane, isobutane, ethane, ethene, propene, isobutene, butadiene, pentane, pentene and pentanes plus.
They may also be referred to as Condensate, just to further complicate the name game!
Natural gas liquids (NGL) range from 1% to 10% of the raw natural gas flow.
Pentanes Plus is a mixture of the heavier liquid hydrocarbons, mostly pentanes, hexane, heptane, octane and heavier.
These are heavier liquid hydrocarbons with typically between 5 and 10 carbon atoms in each molecule.
Natural gasoline is the largest component of pentanes plus.
NGLs are liquid at ambient temperatures, where LNG is only liquid when chilled cryogenically.
Raw natural gas also contains impurities including water vapour, hydrogen sulphide (H2S), carbon dioxide, helium, nitrogen, and other compounds that must be removed to meet quality standards.
What is LPG?
Propane, butane and isobutane, as well as mixtures of these gases, are the three gases that are typically sold as LPG – Liquefied Petroleum Gas.
LPG is a group of flammable hydrocarbon gases that are liquefied through pressurisation and commonly used as fuel.
LPG comes from petroleum refining as well as natural gas processing.
Natural Gas Liquids Fractionation - Stripped from Raw Natural Gas
NGL fractionation is the process used to separate Natural Gas Liquids from natural gas.
Liquid fractionation columns or towers are used to isolate the NGLs from the methane, in a natural gas plant.
In natural gas processing, the gas/oil mixture is piped out of the well and into a gas trap, which separates the stream into crude oil and "wet" gas, which contains LPG and natural gas.
The heavier crude oil sinks to the bottom of the trap and is then pumped into an oil storage tank for refining.
The "wet" gas, off the top of the gas trap, is processed to separate the gasoline (petrol) from the natural gas and LPG.
Processing the Methane (Dry Natural Gas)
Impurities such as water, carbon dioxide, nitrogen and hydrogen sulphide must be removed before either the natural gas (methane) or NGL can be used. Some of these can be sold as by-products.
The refined and purified natural gas, which is mostly methane, is fed into the pipelines that supply our cities and towns.
Distribution of refined natural gas (methane) is typically handled by gas utility companies.
LNG (Liquefied Natural Gas)
Methane gas is processed into LNG by cooling it to −161°C, at which point it becomes a liquid.
This reduces the volume of the natural gas by a factor of more than 600 times as it goes from its gaseous state to liquid.
That's like going from a beach ball to a ping pong ball.
This reduced volume facilitates economical transport by sea or road.
Common LNG uses include industrial applications and long haul trucking.
The technology involved with LNG is generally not cost effective for small volume users, such as homes and small businesses.
For more information, please visit the Elgas LNG web site.
Processing the LPG
LPG processing involves the separation and collection of the gas from its petroleum base.
About 60% is produced from the natural gas stream that comes out of the wellhead.
The other 40% is produced during the crude oil refining process.
The LPG must be separated from an intricate mixture of hydrocarbons, which includes the methane, ethane, ethene, propene, isobutene, butadiene, pentane, and pentene.
The plants that do the processing are frequently called “stripper plants”, as the LPG is stripped from the natural gas flow.
Impurities must also be removed from the propane and butane or they will prevent the LPG from liquefying properly.
The refrigeration technique is common for recovery of LPG from a natural gas stream.
With this technique, they refrigerate the gas stream to obtain the LPG.
Refrigeration is employed in three different processes: expander plants, low temperature separation and combined processes.
Other separation techniques may also be employed, including lean oil absorption.
This LPG can be used as a mixture or further separated into propane, butane and isobutane, as needed.
The LPG enters its own distribution network, where it eventually finds its way to end users, including home LPG and commercial LPG users all around Australia and the world.
Uses of Natural Gas Liquids
Ethane (C2H6) is commonly used in the in the petrochemical industry to produce ethylene, which is used to make plastics like polyethylene.
Propane (C3H8) or LPG is used as a fuel for many residential, commercial and agricultural heat applications, including cooking, hot water systems and heating.
It is also employed as a propellant, refrigerant, vehicle fuel and petrochemical feedstock.
Butane (n-butane) (C4H10) is commonly used as a fuel, propellant and refrigerant, as well as a petrochemical feedstock.
So, it has the same chemical formula as butane – C4H10 – but has a different arrangement of its atoms.
Isobutane is commonly used as a refrigerant and a propellant.
Pentane (C5H12) is are also used in the petrochemical industry to make things like polystyrene foam and other plastic foams.
Hexane (C6H14) is used in gasoline blending, solvents, and other chemical applications.
Heptane (C7H16) is commonly used in solvents. It is undesirable in gasoline, as it is at the zero point of the octane rating scale.
Octane (C8H18) and its isomer, iso-octane, are used as a major components in gasoline (petrol), as they have anti-knock properties.
"Natural gas liquids" is becoming a more commonly referenced term, where previously it was just used within the energy industry.
NGLs include ethane, the traditional LPG gases, and the heavier liquid hydrocarbons.
The terms NGL and LPG are not exactly synonymous but the common LPG gases are included within the wider group of natural gas liquids.
Comments, questions or feedback?
The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.