|Infobox on Propane Gas|
|Example of Propane Gas|
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Propane properties: colourless gas, natural gas odour, non-corrosive.
Propane, the most common liquefied petroleum gas (LP-gas), is one of the nation's most versatile sources of energy and supplies about 4% of our total energy needs.
Propane exists as a liquid and a gas. At atmospheric pressure and temperatures above –44 F, it is a non-toxic, colourless and odourless gas. Just as with natural gas, an identifying odour is added so it can be readily detected. When contained in an approved cylinder or tank, propane exists as a liquid and vapour. The vapour is released from the container as a clean-burning fuel gas. Propane is 270 times more compact as a liquid than as a gas, making it economical to store and transport as a liquid.
Propane is a three-carbon alkane with the molecular formula C3H8, normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central heating. Propane is one of a group of liquefied petroleum gases. The others include butane, propylene, butadiene, butylene, isobutylene and mixtures thereof.
Propane containing too much propene (also called propylene) is not suited for most vehicle fuels. HD-5 is a specification which establishes a maximum concentration of 5% propene in propane. Propane and other LP gas specifications are established in ASTM D-1835. All propane fuels include an odorant, almost always ethanethiol, so that people can easily smell the gas in case of a leak. Propane as HD-5 was originally intended for use as vehicle fuel. HD-5 is currently being used in all propane applications.
Propane is produced as a by-product of two other processes, natural gas processing and petroleum refining. The processing of natural gas involves removal of butane, propane, and large amounts of ethane from the raw gas, in order to prevent condensation of these volatiles in natural gas pipelines. Additionally, oil refineries produce some propane as a by-product of cracking petroleum into gasoline or heating oil. The supply of propane cannot easily be adjusted to meet increased demand, because of the by-product nature of propane production.
Propane is a popular choice for barbecues and portable stoves because the low boiling point of −42 °C makes it vaporize as soon as it is released from its pressurized container. Therefore, no carburetor or other vaporizing device is required; a simple metering nozzle suffices. Propane powers some locomotives, buses, forklifts, taxis and ice resurfacing machines and is used for heat and cooking in recreational vehicles and campers.
Propane is generally stored and transported in steel cylinders as a liquid with a vapour space above the liquid. The vapour pressure in the cylinder is a function of temperature. When gaseous propane is drawn at a high rate, the latent heat of vaporisation required to create the gas will cause the bottle to cool. (This is why water often condenses on the sides of the bottle and then freezes). In addition, the lightweight, high-octane compounds vaporize before the heavier, low-octane ones. Thus the ignition properties change as the tank empties. For these reasons, the liquid is often withdrawn using a dip tube. Propane is used as fuel in furnaces for heat, in cooking, as an energy source for water heaters, laundry dryers, barbecues, portable stoves, and motor vehicles.
Use: Organic synthesis, household and industrial fuel, manufacture of ethylene, extractant, solvent, refrigerant, gas enricher, aerosol propellant, mixture for bubble chambers.
Shipment / Storage
Melting point -188°C
Boiling point -42°C
Flash point -104ºC
Propane is denser than air. If a leak in a propane fuel system occurs, the gas will have a tendency to sink into any enclosed area and thus poses a risk of explosion and fire. The typical scenario is a leaking cylinder stored in a basement; the propane leak drifts across the floor to the pilot light on the furnace or water heater, and results in an explosion or fire. This property makes propane generally unsuitable as a fuel for boats.
Propane is bought and stored in a liquid form (LPG), and thus fuel energy can be stored in a relatively small space. Compressed Natural Gas (CNG), largely methane, is another gas used as fuel, but it cannot be liquefied by compression at normal temperatures, as these are well above its critical temperature. It therefore requires very high pressure to be stored as a liquid, which poses the hazard that, in an accident, just as with any compressed gas tank (such as a CO2 tank used for a soda concession) a CNG tank may burst with great force, or leak rapidly enough to become a self-propelled missile. Therefore, CNG is much less efficient to store, due to the large tank volume required. Another form of storing natural gas is as a low temperature liquid in insulated containers as Liquefied Natural Gas (LNG). This form of storage is at low pressure and is around 3.5 times as efficient as storing it as CNG. Unlike propane, if a spill occurs LNG will evaporate and dissipate harmlessly because it is lighter than air. Propane is much more commonly used to fuel vehicles than is natural gas because the equipment required costs less. Propane requires just 1,220 kilopascals (177 psi) of pressure to keep it liquid at 37.8°C.
Propane gas is stored and handled as a liquid when under pressure inside an LP-gas container. It vaporizes, changing from a liquid to a vapour when released to the atmosphere at a temperature above -44°F. When released into the atmosphere, the gas condenses moisture from the air and thus appears as a white cloud or fog at the point of discharge. The outer edge of this white fog is flammable and will flash if brought in contact with a source of ignition.
LP-gas inside a container is in two states of matter, liquid and vapour. The liquid portion of a container is in the bottom area and the vapour is in the upper area above the liquid. Containers are normally filled to only 80% to allow for vapour expansion due to temperature increase.
Vapour pressure of propane increases as the liquid temperature increases. Propane at -44°F inside a container would register zero pressure. At 32°F, the pressure would increase to 54 psig and at 100°F the pressure would be 205 psig.
Propane is flammable; dangerous fire risk, explosive limits in air 2,4-9,5%.
For overseas carriage aspects of Chemicals, the readers are recommended to acquire or have access to a good chemical dictionary, and a copy of the International Maritime Dangerous Goods (IMDG) Code, issued by the International Maritime Organisation. Also consult the applicable MSDS sheet.
See also: http://www.liquefiedgascarrier.com