Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane, are flammable mixtures of hydrocarbon gases used as fuel in heating appliances, cooking equipment, and vehicles.

 

It is widely used alternative fuel. It has substantial reserves due to its dual origins from natural gas processing and crude oil refining. Liquefied Petrol Gas (LPG) powered passenger cars have about 10% lower tailpipe CO2 emission than comparable gasoline powered cars. When compared to a diesel car, there is no significant CO2 emission reduction per km driven; however, LPG powered vehicles do have substantially lower NOx emissions than diesel powered vehicles.

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It is an inevitable by-product of the crude oil refining process and of natural gas processing. In natural gas processing, the natural gas is cleaned off heavy hydrocarbons such as propane and butane before distribution. About 60% of global LP Gas supply comes from natural gas processing (WLPGA, 2011). In crude oil refining, LPG is a by-product of the refining process. LPG is gaseous at room temperature and changes to a liquid when compressed at moderate pressure or chilled. The chemical composition of LPG can vary, but is usually made up of butane and propane with a 30-99% propane mix. 

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As its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurised steel vessels. They are typically filled to 80–85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (32 psi) for pure butane at 20 °C (68 °F), and approximately 2,200 kilopascals (320 psi) for pure propane at 55 °C (131 °F). LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. There are two main dangers from this. The first is a possible explosion if the mixture of LPG and air is within the explosive limits and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration.

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Liquefied natural gas (LNG) is natural gas that has been cooled to a liquid state, at about -260°Fahrenheit, for shipping and storage. The volume of natural gas in its liquid state is about 600 times smaller than its volume in its gaseous state. This process, which was developed in the 19th century, makes it possible to transport natural gas to places pipelines do not reach and to use natural gas as a transportation fuel.

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For large-volume ocean transport, LNG is loaded onto double-hulled ships, which are used for both safety and insulating purposes. Once the ship arrives at the receiving port, LNG is off-loaded into well-insulated storage tanks, and later re gasified for entrance into a pipeline distribution network.

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LNG can also be shipped in smaller quantities, usually over shorter ocean distances. There is a growing trade in small-scale LNG shipments, which are most commonly made using the same containers used on trucks and in international trade, specially outfitted with cryogenic tanks. Other small-scale LNG activities include “peak-shaver” liquefaction and storage facilities, which can hold gas compactly for when it is needed in local markets in the U.S. during times of peak demand.  LNG is also sometimes imported or exported by truck from this kind of facility.

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Where natural gas pipelines are not feasible or do not exist, liquefying natural gas is a way to move natural gas from producing regions to markets, such as to and from the United States and countries in Asia or Europe. LNG is shipped in special ocean-going ships (tankers) between export terminals, where natural gas is liquefied, and import terminals, where LNG is returned to its gaseous state (re gasified). At an import terminal, it can be injected into pipelines for transmission to distribution companies, industrial consumers, and power plants.

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Most LNG is transported by large ships/tankers called LNG carriers that are equipped with onboard, super-cooled cryogenic tanks. LNG is also transported in relatively small volumes on ships using International Organization for Standardization (ISO)-compliant containers and on trucks.

 

LNG can be used as a fuel for ships, trucks, and buses with specially designed fuel tanks. Some power plants store LNG and use it to generate electricity when electricity demand is high and their natural gas demand exceeds pipeline delivery capacity.