Liquified petroleum gas

Liquified petroleum gas (also called liquefied petroleum gas, liquid petroleum gas, LPG, 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 mixes including both propane and butane, 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. LPG is manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground.

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 should not be 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 liquified gas varies depending on composition, pressure and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapor pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C, and approximately 2.2 megapascals (22 bar) for pure propane at 55 °C. Propane gas is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This should be kept in mind to avoid accidental ignition or suffocation hazards.

Production

LPG is synthesised by refining petroleum or natural gas; it was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed in the United States.

Usage in cars

LPG is widely used as a "green" fuel for internal combustion engines as it decreases exhaust emissions. It has an octane rating (RON) that is between 90 and 110 and an energy content (higher heating value—HHV) that is between 25.5 megajoules per liter (for pure propane) and 28.7 MJ/L (for pure butane.) Toyota made a number of LPG engines in their 1970s M, R, and Y engine families.

Currently, a number of automobile manufacturers—Citroën, Daewoo, Fiat, Ford, Hyundai, Opel/Vauxhall, Peugeot, Renault, Saab and Volvo—have OEM bi-fuel models that will run equally well on both LPG and gasoline.Vialli have OEM LPG powered scooters and LPG powered mopeds that run equally well on LPG.

LPG is popular in Australia (due to it being less than half the price of petrol), with the four major local manufacturers (Ford, Holden, Mitsubishi and Toyota) offering it in some models of their locally made large family sedans. All are 'dual fuel' vehicles, with the exception of Ford, whose Falcon LPG model (the engine is called the E-Gas) runs LPG only. LPG is especially popular with taxis, with a large number of Australian cabs (typically Ford Falcons) being LPG-fuelled. However, whilst LPG is excise-free at the present time, there are plans to introduce an excise on LPG of 12 cents per litre (as opposed to the 38 cpl excise on petrol), starting from 2011.

LPG as cooking fuel

According to the 2001 Census of India, 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001 ^*. 76.64% of such households were from urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in rural Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the urban middle class voting pattern.

LPG was once a popular cooking fuel in Hong Kong; however, the continued expansion of town gas to buildings has reduced LPG usage to less than 24% of residential units.

LPG as refrigerant

Highly refined LPG — nearly pure propane with an odorant added — can be effectively used as a replacement refrigerant in systems designed for CFC-12, R-22 and R-134a refrigerants. It is not considered a greenhouse gas, and thus can be handled without special equipment to prevent its escape into the atmosphere. It is non-toxic (except for narcotic and asphyxiating properties common to many gases), and in highly refined form it exhibits a relatively high flash point of 891 °C (1635 °F), higher than that of R-134a. If it should burn, it produces carbon dioxide and water vapor (and soot), whereas R-134a, now commonly used in automotive applications, produces thermal decomposition products including hydrogen fluoride and carbon dioxide.

LPG and SNG

LPG has a higher calorific value (94 MJ/m³) than natural gas (methane) (38 MJ/m³), which means that LPG can not simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the LPG. The method for determining the mixing ratios is by calculating the Wobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable.

LPG-based SNG is used in emergency backup systems for many public, industrial, and military installations, and many utilities use LPG peak shaving plants in times of high demand to make up shortages in natural gas supplied to their distributions systems. LPG-SNG installations are also used during initial gas system introductions, when the distribution infrastructure is in place before gas supplies can be connected. Developing markets in India and China (among others) use LPG-SNG systems to build up customer bases prior to expanding existing natural gas systems.

Fire Risk and Mitigation

1. The Situation and Risk:
- LPG containers that are subjected to fire of sufficient duration and intensity can BLEVE. This is typically a concern for large refineries and petrochemical plants that maintain very large containers. If they are cylindrical and horizontal, they are referred to as "cigars", whereas circular one as are "spheres". It is not unusual for large, spherical LPG containers to have up to a 15cm steel wall thickness. Usually, such large LPG containers can be seen whilst driving past petrochemical complexes. One can also see them in transit, on trains or lorries (trucks). Ordinarily, they are equipped with an approved pressure relief valve on the top, in the centre. Particularly in outdoor petrochemical facilities, the hazard stems from accidental spills of hydrocarbons, which may catch on fire, thus immersing an LPG container. Whilst the contents of the container are ordinarily cool, an external fire will provide energy to the contents, which are subject to the basic gas laws, meaning that the temperature increases, and so does the pressure. The relief valve on the top is designed to vent off excess pressure in order to prevent the rupture of the tank itself. Given a fire of sufficient duration and intensity, the pressure being generated by the boiling and expanding gas can exceed the ability of the valve to vent the excess. When that occurs, the tank itself must rupture, which can literally make "rockets" out of the parts that come off, as each still contain fuel, which is still subject to the common laws governing gas. LPG tanks have been known to have dominoe effects upon one another, once engaged in a significant fire, which can cause catastrophic projectile damage to the surrounding areas.

2. Mitigation
- Mitigation measure are really quite simple. One must separate the LPG tanks from potential sources of fire. In the case of rail transport, for instance, it would be best to make sure that LPG tanks are staggered, so that other goods are put in between the LPG tanks.

In the case of new LPG containers, one may simply bury them, only leaving valves and armatures exposed. Great care must be taken there though, as mechanical damage has been known to occur to the primers, which has resulted in hazardous corrosion of the containers. For the buried container, only the exposed parts can be treated with approved fireproofing materials, such as intumescent and or endothermic coatings, or even fireproofing plasters. Speciality removable covers exist for easy access to the dials and components that must be accessed for proper maintenance and operation of the equipment. LPG containers are subject to significant motion due to expansion, contraction, filling and emptying - even with very thick steel walls. Whilst one may calculate and justify the use of inorganic plasters to cover entire spheres, it can be difficult to keep plasters operable for extended periods of time. Major errors have also been made in the past in this field, as the presumption was that the steel substrate would be adequately protected from rusting through the use of alkaline plasters, this alakalinity does not typically have a permanent character, which means that waterproofing with high quality epoxy primers is very important. By contrast, the intumescent and endothermic coatings are usually epoxy based in the first place, meaning that corrosion of the substrate is no problem in the first place. Fireproofing, not unlike all passive fire protection products, are subject to stringent bounding. The problem with this is though, that exterior structures of this nature are not subject to the building code or the fire code, meaning that one still sees the majority of LPG containers without any fireproofing whatsoever, as there are often no local regulations, let alone any Authority Having Jurisdiction, apart from an insurance inspector, to force owners to use the proper mitigation methods. Insurance companies are also in a competitive quandary, where such items are concerned, as they compete not only on the basis of rates, but also on the strictness of the demands by their inspectors. LPG vessel fireproofing tests are varied. The only realistic exposure offered done at the Braunschweig test facility of "BAM" Berlin BAM's procedure is to expose a small LPG container to the hydrocarbon test curve and to quantify the results. North American methods are based on UL1709 bounding and to be sure that the product one chooses has undergone product certification, whereby the original test included the environmental exposures that the product will be exposed to during operations. Particularly with organic products, such as the endothermic and intumescent ones, one must closely review the ageing criteria and be able to quantify how long the product is expected to be operable for. This is where UL1709 "shines". Anything that can withstand the full battery of environmental exposures prior to the actual fire test, is a very tough product indeed. Likewise, the DIBt [http://www.dibt.de/" target="_blank" >^* ageing qualifications for intumescents have proven to be very reliable. With close attention to the bounding and coverage of ageing and environmental exposures, it is absolutely possible to buy a lot of time for firefighting measures to relieve the LPG containers of the energy exposure from accidental fires.

External links

LP Gas Association — LPG in the UK
BoostLPG — Autogas in the UK including List of LPG fuelling stations in the UK
About LPG
Fuelture; UK automotive LPG site
Go LPG — List of LPG fuelling stations in the UK
RPiV8.com — UK site with a lot of information and advice on LPG.
LPG Autogas Australia — LPG Autogas in Australia.
UL1709 ^*
BAM Berlin ^*
Deutsches Institut für Bautechnik (DIBt) ^*
^* Poten & Partners: A Collection of Articles Relating to LPG

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