Propane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves and residential central heating.
When used as vehicle fuel, it is commonly known as liquefied petroleum gas (LPG or LP-gas), which can be a mixture of propane along with small amounts of propylene, butane, and butylene. An odorant such as ethanethiol or thiophene is added so that people can easily smell the gas in case of a leak.
History
Propane was first identified as a volatile component in gasoline by Dr. Walter O. Snelling of the U.S. Bureau of Mines in 1910. The volatility of these lighter hydrocarbons caused them to be known as "wild" because of the high vapor pressures of unrefined gasoline. On March 31 the New York Times reported on Dr. Snelling's work with liquefied gas and that "...a steel bottle will carry enough to light an ordinary home for three weeks."
It was during this time that Dr. Snelling, in cooperation with Frank P. Peterson, Chester Kerr and Arthur Kerr, created ways to liquefy the LP Gases during the refining of natural gasoline. Together they established American Gasol Co., the first commercial marketer of propane. Dr. Snelling had produced relatively pure propane by 1911, and on March 25, 1913 his method of processing and producing LP Gases was issued patent #1,056,845. A separate method of producing LP Gas through compression was created by Frank Peterson and patented in 1912.
The 1920s saw increased production of LP Gas, with the first year of recorded production totaling 223,000 gallons in 1922. In 1927, annual marketed LP Gas production reached one million gallons, and by 1935, the annual sales of LP Gas had reached 56 million gallons. Major industry developments in the 1930s included the introduction of railroad tank car transport, gas odorization and the construction of local bottle-filling plants. The year 1945 marked the first year that annual LP Gas sales reached a billion gallons. By 1947, 62% of all U.S. homes had been equipped with either natural gas or propane for cooking.
In 1950, 1,000 propane-fueled buses were ordered by the Chicago Transit Authority, and by 1958, sales in the U.S. had reached 7 billion gallons annually. In 2004 it was reported to be a growing $8-billion to $10-billion industry with over 15 billion gallons of propane being used annually in the U.S.
The "prop-" root found in propane and other three-carbon chains was derived from propionic acid.
Properties and reactions
Propane undergoes combustion reactions in a similar fashion to other alkanes. In the presence of excess oxygen, propane burns to form water and carbon dioxide.
When not enough oxygen is present for complete combustion, incomplete combustion occurs when propane burns and forms water, carbon monoxide, carbon dioxide, and carbon.
Unlike natural gas, propane is heavier than air (1.5 times as dense). In its raw state, propane sinks and pools at the floor. Liquid propane will flash to a vapor at atmospheric pressure and appears white due to moisture condensing from the air.
When properly combusted, propane produces about 50 MJ/kg. The gross heat of combustion of one normal cubic meter of propane is around 91 megajoules
Propane is nontoxic; however, when abused as an inhalant it poses a mild asphyxiation risk through oxygen deprivation. Commercial products contain hydrocarbons beyond propane, which may increase risk. Commonly stored under pressure at room temperature, propane and its mixtures expand and cool when released and may cause mild frostbite.
Propane combustion is much cleaner than gasoline combustion, though not as clean as natural gas combustion. The presence of C–C bonds, plus the multiple bonds of propylene and butylene, create organic exhausts besides carbon dioxide and water vapor during typical combustion. These bonds also cause propane to burn with a visible flame.
Greenhouse gas emissions factors for propane are 62.7 kg CO 2 / mBTU or 1.55 kg of CO 2 per litre or 73.7 kg / GJ.
Energy content
The energy density of propane is 46.44 megajoules per kilogram (91,690 BTU per gallon).
Uses
Propane is used as fuel in cooking on many barbecues, portable stoves and in motor vehicles. The ubiquitous 4.73-gallon (20 lb.) steel container is often dubbed a "barbecue tank". Propane remains a popular choice for barbecues and portable stoves because its low boiling point of −42 °C (−43.6 °F) 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.
In rural areas of North America, propane is used in furnaces (including livestock facilities), cooking stoves, water heaters, laundry dryers, grain dryers, and other heat-producing appliances. When used for heating or grain drying it is usually stored in a large, permanently-placed cylinder which is recharged by a propane-delivery truck. As of 2000, 6.9 million American households use propane as their primary heating fuel.
Commercially-available "propane" fuel, or LPG, is not pure. Typically in the USA and Canada, it is primarily propane (at least 90%), with the rest mostly butane and propylene (5% maximum), plus odorants. This is the HD-5 standard, ( H eavy D uty- 5 %maximum allowable propylene content) written for internal combustion engines. LPG, when extracted from natural gas, does not contain propylene. LPG, when refined from crude oil does contain propylene. Not all products labelled "propane" conform to this standard. In Mexico, for example, the butane content is much higher.
Domestic and industrial fuel
In North America, local delivery trucks called "bobtails", with an average tank size of 3,000 gallons, fill up large tanks (sometimes called pigs ) that are permanently installed on the property, or other service trucks exchange empty cylinders of propane with filled cylinders. Large tractor-trailer trucks called "cargo-liners", with an average tank size of 10,000 gallons, transport the propane from the pipeline or refinery to the local delivery plant. The bobtail and transport are not unique to the North American market, though the practice is not as common elsewhere, and the vehicles are generally referred to as tankers . In many countries, propane is delivered to consumers via small or medium-sized individual tanks.
Propane use is growing rapidly in non-industrialized areas of the world. Propane is replacing wood and other traditional fuel sources in such places, where it is now sometimes called "cooking gas". North American barbecue grills powered by propane cannot be used overseas. The "propane" sold overseas is actually a mixture of propane and butane. The warmer the country, the higher the butane content, commonly 50/50 and sometimes reaching 75% butane. Usage is calibrated to the different-sized nozzles found in non-U.S. grills. Americans who take their grills overseas — such as military personnel — can find U.S.-specification propane at AAFES military post exchanges.
North American industries using propane include glass makers, brick kilns, poultry farms and other industries that need portable heat.
Refrigeration
Propane is also instrumental in providing off-the-grid refrigeration, usually by means of a gas absorption refrigerator.
Blends of pure, dry "isopropane" (R-290a) (commercial term used to describe isobutane/propane mixtures) and isobutane (R-600a) have negligible Ozone depletion potential and very low Global Warming Potential and can serve as a functional replacement for R-12, R-22, R-134a, and other chlorofluorocarbon or hydrofluorocarbon refrigerants in conventional stationary refrigeration and air conditioning systems.
In motor vehicles
Such substitution is widely prohibited or discouraged in motor vehicle air-conditioning systems, on the grounds that using flammable hydrocarbons in systems originally designed to carry non-flammable refrigerant presents a significant risk of fire or explosion.
Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons. One particular test was conducted by a professor at the University of New South Wales that unintentionally tested the worst case scenario of a sudden and complete refrigerant loss into the passenger compartment followed by subsequent ignition. He and several others in the car sustained burns to the face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window.
Vehicle fuel
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