Natural Gas Terminology

NGL (Natural Gas Liquids).
Heavier gaseous hydrocarbons: ethane (C2H6), propane (C3H8), normal butane (n-C4H10), isobutane (i-C4H10), pentanes and even higher molecular weight hydrocarbons. When processed and purified into finished by-products

LNG (Liquefied natural gas)
LNG is natural gas (primarily methane, CH4) that has been converted to liquid form for ease of storage or transport. Liquefied natural gas takes up about 1/600th the volume of natural gas at a stove burner tip. It is odorless, colorless, non-toxic and non-corrosive. Hazards include flammability, freezing and asphyxia.
The liquefication process involves removal of certain components, such as dust, helium, water, and heavy hydrocarbons, which could cause difficulty downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure (Maximum Transport Pressure set around 25 kPa (3.6 psi)) by cooling it to approximately −163 °C (−260 °F). The reduction in volume makes it much more cost-efficient to transport over long distances where pipelines do not exist. Where moving natural gas by pipelines is not possible or economical, it can be transported by specially designed cryogenic sea vessels (LNG carriers) or cryogenic road tankers.
The energy density of LNG is 60% lower than that of diesel fuel.[1]

LPG (Liquefied petroleum gas)
LPG also called GPL, LP Gas, or autogas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer.
Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and the more common, mixes including both propane (60%) and butane (40%), depending on the season—in winter more propane, in summer more butane. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589.
At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is supplied in pressurised steel bottles. In order to allow for thermal expansion of the contained liquid, these bottles are not filled completely; typically, they are filled to between 80% and 85% of their capacity. The ratio between the volumes of the vaporised 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 (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) for pure propane at 55 °C (131 °F). LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with.
LPG is the lowest carbon emitting hydrocarbon fuel available in rural areas, emitting 19 percent less CO2 per kWh than oil, 30 percent less than coal and more than 50 percent less than coal- generated electricity distributed via the grid.
LPG has a typical specific calorific value of 46.1MJ/kg compared to 42.5MJ/kg for diesel and 43.5MJ/kg for premium grade petrol (gasoline).[1] However, its energy density per unit volume is lower than either petrol or diesel.

Sumber : wikipedia.org