|
|
|
(LPG), (CNG) & (LNG) |
|
|
|
3.4 LPG, CNG & LNG
- 3.4.1 Liquid Petroleum Gas (LPG)
LPG is produced (synthesised) by refining petroleum or natural gas and consists of mainly propane or butane or a mixture of both.
It was first produced in 1910.
LPG becomes a liquid either by being chilled or by just applying pressure.
For pure Butane: 220 kilopascals (2.2 bar) at 20 degrees C (68F), or less than –2 degrees C at standard pressure.
For pure Propane: 2.2 megapascals (22 bar) at 55 degrres C (131F), or less than –42 degrees C at standard pressure.
In 1931 Shell’s “Agnita” became the first ship purpose- built to carry LPG.
LPG is heavier than air. Any leaks settle on the floor.
When LPG is used as a vehicle fuel is a often called “Autogas”. Its use decreases CO2 exhaust emissions by about 20%.
Citroen, Fiat, Ford, Hindustan Motors, Holden, Opel, Peugeot, Renault, Saab and Volvo produce cars that run on both petrol and LPG.
EN 589 (2004) is the European standard for Autogas.
LPG mileage can vary by more than 100%, dependant on the ambient temperature. More miles being achieved as the temperature reduces.
Early duel fuel, petrol/LPG, cars used about 25% more fuel than “petrol” only cars. Fuel economy in some modern LPG only cars is comparable with petrol powered cars.
3.4.2 Compressed Natural Gas (CNG)
CNG is natural gas that has been processed and pressurized, typically between 3,000 and 4,000 pounds per square inch (205 to 275 bar). It can be used as a substitute for diesel or petrol. Natural gas consists mainly of methane (70-90%), ethane (5-15%), propane (less than 5%) and smaller quantites of carbon dioxide, nitrogen, helium and hydrogen sulfide. When natural gas is used as a fuel all other gases, other than methane, are removed. Vehicles using CNG require more space for fuel storage than those using petrol or diesel which impacts on the shape of the smaller vehicles.
3.4.3 Liquefied Natural Gas (LNG)
In addition to being stored as compressed gas (CNG), natural gas can also be stored in a liguid form called Liquefied Natural Gas (LNG). It was first produced in about 1917. LNG is processed natural gas that has been reduced to −265 degrees F (−165 C) at atmospheric pressure. If not kept at or below this temperature the liquid will boil and become a gas. A liquefaction process purifies LNG to almost 100% methane. CNG can be produced from LNG. When natural gas becomes LNG it takes up only about 1/600th of the space. The first ship to carry LNG was a converted cargo vessel, the “Methane Pioneer, in 1959. In 1964 the “Methane Princess” and the “Methane Progress”, both managed by Shell, became the first ships purpose- built to carry LNG.
|
|
