Natural gas liquids or simply NGLs are used today in almost all sectors of the economy, and a small share of the production (about 10%) is exported.
Natural Gas Liquids Definition?
Natural gas liquids (NGLs) is a term used to describe hydrocarbons that were removed in a liquid state from a hydrocarbon stream that is in vapor phase.
NGLs are composed exclusively from carbon and hydrogen, and contain the same family of molecules like natural gas and crude oil.
NGLs include: methane (C1H4), ethane (C2H6), propane (C3H8), butane and isobutane (C4H10), pentane (C5H12), hexane (C6H14), heptane (C7H16), etc.
As we can see, each successive NGL has an additional carbon molecule and different chemical properties.
Types of Natural Gas Liquids
Natural gas liquids can be found in gaseous state in the raw natural gas that is produced by three types of gas wells:
1. Crude oil wells
Crude oil wells also produce raw natural gas that is called associated gas. In the underground formation, the raw natural gas can be found separated or dissolved in crude oil.
2. Dry gas wells
This type of gas wells produce only raw natural gas, which does not contain hydrocarbon liquids, and is called non-associated gas.
3. Condensate wells
Condensate wells produce raw natural gas and natural gas liquids. This gas is also called associated gas or wet gas.
Condensate produced from oil wells is often called lease condensate.
All natural gas liquids (NGLs) have added value based on BTU (British Thermal Unit).
Net BTU Value of Natural Gas Liquids.
Natural gas contains mainly methane, but also a number of natural gas liquids (some of them more common, such as ethane, propane and butane).
Hydrocarbon liquids produced from natural gas
- 1. Ethane – C2H6.
- 2. Propane – C3H8.
- 3. Butane – C4H10.
- 4. Isobutane – is an isomer of butane.
- 5. Pentanes – C5H12 (“C5+”).
- 6. Natural gasolines (C5 and some C6 – C9).
- 7. Condensate (C6+).
Sources, Production and Types of NGLs Processing Plants
1. Sources of NGLs
The sources of natural gas liquids have been increased over the last few years and will continue to increase in the next two to three decades or at least until mankind will rely on natural gas for energy and heat production on the planet.
We have this way crude oil and lease condensate, raw natural gas, biofuels, unconventional oils, CTL (coal-to-liquids) and GTL (gas-to-liquids).
2. Production Process of NGLs
NGLs must be removed from the gas stream, otherwise the BTU content will be too volatile for any type of burner tip use.
In processing plants, from the raw natural gas, the contaminants and the inert gases are removed, to extract as much heavy hydrocarbons possible and sell them as ethane, propane, butane, etc.
The basic operations of the processing plants include the removal of the heavy hydrocarbons, “purifying” the gas stream, etc.
Removing Heavy Hydrocarbons
The heavy hydrocarbons are removed from the gas stream to protect the burnertip from volatile fuels with high BTU content such as (propane and butane).
By removing the heavy hydrocarbons, the processing plant manages to produce the much needed natural gas liquids such as: ethane, propane, butane, iso-butane, natural gasolines, etc.
To extract heavier hydrocarbons, the processing plant uses various processes such as condensation (the majority of NGLs are produced through the condensation process), absorption (uses oils that absorb some of the light hydrocarbons from the natural gas stream), and fractionation (NGLs are removed here from a composite stream into the various fractions like ethane, propane, butane, etc.).
“Purifying” the Gas Stream
The raw natural gas comes out from the well and contains contaminants and inert gases that need to be removed.
This way, the processing plant removes as much of the water as possible (H2O) trough dehydration (glycol absorption), hydrogen sulfide (H2S) using amine treatment, carbon dioxide (CO2) and nitrogen (N) using nitrogen rejection units.
3. Types of Processing Plants
Separator Tower Plant
This type of processing plant flow the gas stream though the bottom of the tower, and because the tower uses collector trays, while methane will rise to the top of the tower, the heavier hydrocarbons will settle on trays.
The plant will vary pressures and temperatures by using compressors that will recirculate the natural gas throughout the processing plant, and “re-boilers” that are furnaces fueled by natural gas and used to heat up the natural gas stream and then cool it down hoping to extract as much heavy hydrocarbons as possible to produce natural gas liquids.
Cryogenic Plant
Cryogenic processing plants, heat the natural gas and then drop the temperature to a very low level.
This processing plant uses refrigerants and turbine expanders to cool down the natural gas and expand the stream to produce condensation that will extract the NGLs out.
The natural gas is recirculated through the processing plant as many times as possible, until it gets about 98 percent purity of the methane, and only after that is returned to the transmission pipe.
The NGLs collected this way are brought to market.
“Straddle” Plant
This type of processing plant “straddles” the transmission pipeline itself, extracts the natural gas from the pipeline, processes it, and then re-delivers the gas to the pipeline.
Types of NGLs and their Uses
1. Propane
Propane represents about 40% of the NGL market in the U.S. and is primarily used for home heating and cooking.
Is also used as chemical feedstock for propylene that is used in plastics production.
2. Ethane
Ethane represents about 25% of the NGL market in the United States, and is primarily used as chemical feedstock (converted or cracked) for ethylene and propylene production, which is then used to produce plastics.
This NGL is very price dependent and is rarely used as a fuel source.
Can also be left in the gas stream as methane (ethane rejection).
3. Butane
Butane or n-butane is mainly used for gasoline blending (about 85% of the production).
This NGL is mostly used in the winter, when the RVP (Reid Vapor Pressure) of gasoline is high.
RVP refers to the ability of the gasoline to vaporize at atmospheric pressure.
We don’t want gasoline to have a high vapor pressure during the winter, therefore butane is added to gasoline to avoid the escaping of the fuel into the atmosphere.
Butane is also used as catalyst in crude refining, as lighter fluid, as propellant in aerosol sprays, as bottled gas and for household cooking, and also as refrigerant.
Iso-Butane is an isomer of butane and has similar uses as butane such as: gasoline blending, chemical feedstock, as refrigerant (R600a for automobiles) and as additive to improve gasoline octane (isooctane).
4. Natural Gasolines or “Pentanes”
These NGLs have the chemical symbols C5+ and are primarily used for gasoline blending (to stabilize the RVP of gasoline during the summer).
Pentanes are also used for ethylene production, as industrial solvents, to make ethanol undrinkable (denaturant for ethanol) and to dilute crude.
What is the Difference Between NGLs and LNG?
Natural gas liquids (NGLs) refer to a wide range of heavier hydrocarbons like oil and natural gas obtained from but runed from gaseous state into liquid state. Examples on NGLs: ethane, propane, butane, isobutane, and pentane.
Liquefied natural gas (LNG) refers to a gas (methane) that is turned from gaesous form into liquid form to ease the transportation.
Final thought
The extraction and use of NGLs will stop only when mankind will stop using oil and natural gas as main fuels for energy and heat production.
The wide spread of the electric vehicles that will replace the conventional vehicles with internal combustion engine will reduce the use of gasoline and diesel fuels, which will decrease the production of oil and NGLs on the planet.
Less oil means less air, water and soil pollution and a healthier environment for mankind.
