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Propane
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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, barbecues, portable stoves and residential central heating.
When used as vehicle fuel, it is commonly known as liquified petroleum gas (LPG or LP-gas), which can be a mixture of propane along with small amounts of propylene, butane, and butylene. The odorant ethanethiol is also added so that people can easily smell the gas in case of a leak.
Properties and reactions
Propane undergoes combustion reactions in a similar fashion to other alkanes.
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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, barbecues, portable stoves and residential central heating.
When used as vehicle fuel, it is commonly known as liquified petroleum gas (LPG or LP-gas), which can be a mixture of propane along with small amounts of propylene, butane, and butylene. The odorant ethanethiol is also added so that people can easily smell the gas in case of a leak.
Properties and reactions
Propane undergoes combustion reactions in a similar fashion to other alkanes. In the presence of excess methane, propane burns to form water and carbon dioxide.
- C3H8 + 5 O2 ? 3 CO2 + 4 H2O + heat
- Propane + Oxygen ? Carbon Dioxide + Water
When not enough oxygen is present for complete combustion, incomplete combustion occurs when propane burns and forms water, carbon monoxide, carbon dioxide, and carbon.
- C3H8 + 3.5 O2 ? CO2 + CO + C + 4 H2O + heat
- Propane + Oxygen ? Carbon Dioxide + Carbon Monoxide + Carbon + Water
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 CO2/ mBTU or 1.55 kg of CO2 per litre or 73.7 kg / GJ.
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 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 many rural areas of North America, propane is used in furnaces, cooking stoves, water heaters, laundry dryers, and other heat-producing appliances. , 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, (Heavy Duty-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 unintentionaly 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 their face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window.
Vehicle fuel
Propane is also being used increasingly for vehicle fuels. In the U.S., 190,000 on-road vehicles use propane, and 450,000 forklifts use it for power. It is the third most popular vehicle fuel in America, behind gasoline and diesel. In other parts of the world, propane used in vehicles is known as autogas. About 9 million vehicles worldwide use autogas.
The advantage of propane is its liquid state at a moderate pressure. This allows fast refill times, affordable fuel tank construction, and ranges comparable to (though still less than) gasoline. Meanwhile it is noticeably cleaner (both in handling, and in combustion), results in less engine wear (due to carbon deposits) without diluting engine oil (often extending oil-change intervals), and until recently was a relative bargain in North America. Octane rating is a noticeably higher 110. However, public filling stations are still rare. Many converted vehicles have provisions for topping off from "barbecue bottles". Purpose-built vehicles are often in commercially-owned fleets, and have private fueling facilities.
Propane is generally stored and transported in steel cylinders as a liquid with a vapor space above the liquid. The vapor 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 extreme cases this may cause such a large reduction in pressure that the process can no longer be supported. 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.
Other
- Propane is used as a feedstock for the production of base petrochemicals in steam cracking.
- Propane is used in some flamethrowers, as the fuel, or as the pressurizing gas.
- Some propane becomes a feedstock for propyl alcohol, a common solvent.
- Propane is the primary fuel for hot air balloons.
- It is used in semiconductor manufacture to deposit silicon carbide.
- Propane is mixed with silicone to form a propellant (sold as green gas) which is used to power gas guns used in airsoft combat gaming.
- Liquid propane is commonly used in theme parks and in the movie industry as an inexpensive, high-energy fuel for explosions and other special effects.
Propane risks and alternate gas fuels
Propane is heavier 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.
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 requires very high pressure to liquefy (which is dangerous). Therefore, CNG is much less efficient to store due to the large tank volume required. Thus propane is much more commonly used to fuel vehicles than natural gas and requires just of pressure to keep it liquid at .
Propane Tank Remainder Measurement
The fluid level in a propane tank can be measured with an internal magnetic "float". An external gauge can then sense the location of the float within the tank. This magnetic float-gauge system cannot accurately measure the total propane amount, since the gaseous portion of the propane within the tank is neglected from measurement.
The most accurate way to measure the propane left in a propane tank is to weigh it. Stamped into the side of the tank should be the letters TW followed by a number. This number is the weight in pounds of tank when empty, or its tare weight. A typical 5 gallon propane tank may have a tare weight of 17.2 pounds. If this tank were weighed at 24.2 lbs, it follows that there are 7 pounds of propane stored in the tank (24.2 lbs - 17.2 lbs = 7 lbs).
Each gallon of liquid propane weighs 4.23 lbs, meaning the tank in this example contains 1.66 gallons of propane (7 ÷ 4.23 ˜ 1.66).
A gallon of propane contains 91,690 BTUs. Multiplying this number by the number of gallons in the tank results in 152,205 BTUs of thermal energy (1.66 × 91,690 = 152,205).
The running time of a particular appliance can then be calculated if the BTU consumption of the appliance is known. This number, given in BTUs per hour, can usually be found on the appliance or from the manufacturer. Continuing this example, an appliance that consumes 12,000 BTUs per hour would provide 12.68 hours of operation (152,205 ÷ 12,000 ˜ 12.68).
Sources
Propane is produced as a byproduct 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 to prevent condensation of these volatiles in natural gas pipelines. Additionally, oil refineries produce some propane as a by-product of production of cracking petroleum into gasoline or heating oil.
The supply of propane cannot be easily adjusted to account for increased demand because of the by-product nature of propane production. About 90% of U.S. propane is domestically produced.
The United States imports about 10% of the propane consumed each year with about 70% of that coming from Canada via pipeline and rail. The remaining 30% of imported propane comes to the United States from other sources via ocean transport.
After it is produced, North American propane is stored in huge salt caverns located in Fort Saskatchewan, Alberta, Canada; Mont Belvieu, Texas and Conway, Kansas. These salt caverns were hollowed out in the 1940s and can store up to 80 million barrels of propane, or more. When the propane is needed, most of it is shipped by pipelines to other areas of the Midwest, the North and the South, for use by customers. Propane is also shipped by barge and rail car to selected U.S. areas.
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 [gas] 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.
Its name was originally derived from propionic acid.
Retail cost
United States
In 2008, propane cost $42.67 per 1 million BTUs when used for heating.
See also
External links
- *
- Descriptive Breakdown of Propane Characteristics
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