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LPG storage spheresTwo 45 kg (99 lb) LPGgas cylinders inNew Zealand used for domestic supplyLPG minibuses inHong KongA dual fuel LPG-poweredFord Falcon taxicab inPerth, AustraliaTank cars in a Canadian train for carrying liquid petroleum gas by rail
Varieties of LPG that are bought and sold include mixes that are mostly propane (C 3H 8), mostly butane (C 4H 10), and, most commonly, mixes including both propane and butane. In the northern hemisphere winter, the mixes contain more propane, while in summer, they contain more butane.[8][9] In theUnited States, mainly two grades of LPG are sold: commercial propane and HD-5. These specifications are published by the Gas Processors Association (GPA)[10] and the American Society of Testing and Materials.[11] Propane/butane blends are also listed in these specifications.
Propylene,butylenes and various other hydrocarbons are usually also present in small concentrations such asC2H6,CH4, andC3H8. HD-5 limits the amount of propylene that can be placed in LPG to 5% and is utilized as an autogas specification.[12] A powerfulodorant,ethanethiol, is added so that leaks can be detected easily. The internationally recognized European Standard is EN 589. In the United States,tetrahydrothiophene (thiophane) oramyl mercaptan are also approved odorants,[13] although neither is currently being utilized.
LPG is prepared byrefiningpetroleum or "wet"natural gas, and is almost entirely derived fromfossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. It was first produced in 1910 byWalter O. Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of all energy consumed, and burns relatively cleanly with nosoot and very littlesulfur emission. As it is a gas, it does not pose ground orwater pollution hazards, but it can causeair pollution. LPG has a typical specificcalorific value of 46.1 MJ/kg compared with 42.5 MJ/kg forfuel oil and 43.5 MJ/kg for premium gradepetrol (gasoline).[14] However, itsenergy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as itsrelative density is lower (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L forgasoline). As the density and vapor pressure of LPG (or its components) change significantly with temperature, this fact must be considered every time when the application is connected with safety orcustody transfer operations,[15] e.g. typical cuttoff level option for LPG reservoir is 85%.
Besides its use as an energy carrier, LPG is also a promising feedstock in the chemical industry for the synthesis of olefins such as ethylene and propylene.[16][17]
As its boiling point is below roomtemperature, LPG will evaporate quickly at normal temperatures andpressures and is usually supplied in pressurizedsteelvessels. They are typically filled to 80–85% of their capacity to allow forthermal expansion of the contained liquid. The ratio of the densities of the liquid and vapor varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called itsvapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (32 psi) for purebutane at 20 °C (68 °F), and approximately 2,200 kilopascals (320 psi) for purepropane at 55 °C (131 °F). LPG in its gaseous phase is still heavier thanair, unlikenatural gas, and thus will flow along floors and tend to settle in low spots, such asbasements. There are two main dangers to this. The first is a possibleexplosion if the mixture of LPG and air is within theexplosive limits and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration.
A full LPGgas cylinder contains 86% liquid; theullage volume will contain vapour at a pressure that varies with temperature.[18]
LPG has a wide variety of uses in many different markets as an efficient fuel container in the agricultural, recreation, hospitality, industrial, construction, sailing and fishing sectors. It can serve as fuel for cooking, central heating andwater heating and is a particularly cost-effective and efficient way to heat off-grid homes.
LPG is used for cooking in many countries for economic reasons, for convenience or because it is the preferred fuel source.
In India, nearly 28.5 million metric tons of LPG were consumed in the 2023–24 financial year in the domestic sector, mainly for cooking.[19] In 2016, the number of domestic connections was 215 million (i.e., one connection for every six people) with a circulation of more than 350 million LPG cylinders.[20] Most of the LPG requirement is imported. Piped city gas supply in India is not yet developed on a major scale. LPG is subsidised by the Indian government for domestic users. An increase in LPG prices has been a politically sensitive matter in India as it potentially affects themiddle class voting pattern.
LPG was once a standard cooking fuel inHong Kong; however, the continued expansion oftown gas to newer buildings has reduced LPG usage to less than 24% of residential units. However, other than electric, induction, or infrared stoves, LPG-fueled stoves are the only type available in most suburban villages and many public housing estates.
LPG is the most common cooking fuel inBrazilian urban areas, being used in virtually all households, with the exception of the cities of Rio de Janeiro and São Paulo, which have a natural gas pipeline infrastructure. Since 2001, poor families receive a government grant ("Vale Gás") used exclusively for the acquisition of LPG. Since 2003, this grant is part of the government's main social welfare program ("Bolsa Família"). Also, since 2005, the national oil companyPetrobras differentiates between LPG destined for cooking and LPG destined for other uses, establishing a lower price for the former. This is a result of a directive from the Brazilian federal government, but its discontinuation is currently being debated.[21]
LPG cylinders inIndiaLiquefied petroleum gas tank on a rural farm
Predominantly in Europe and rural parts of many countries, LPG can provide an alternative toelectric heating,heating oil, orkerosene. LPG is most often used in areas that do not have direct access to pipednatural gas. In the UK about 200,000 households use LPG for heating.
LPG can be used as a power source forcombined heat and power technologies (CHP). CHP is the process of generating both electrical power and useful heat from a single fuel source. This technology has allowed LPG to be used not just as fuel for heating and cooking, but also for decentralized generation of electricity.
Bottling LPG in the Marshall Islands for storage
LPG can be stored in a variety of manners. LPG, as with otherfossil fuels, can be combined withrenewable power sources to provide greater reliability while still achieving some reduction in CO2 emissions. However, as opposed towind andsolar renewable energy sources, LPG can be used as a standalone energy source without the prohibitive expense of electricalenergy storage. In many climates, renewable sources such as solar and wind power would still require the construction, installation and maintenance of reliable baseload power sources such as LPG fueled generation to provide electrical power during the entire year. 100% wind/solar is possible, the caveat being that the expense of the additional generation capacity necessary to charge batteries plus the cost of battery electrical storage makes this option economically feasible in only a minority of situations.[citation needed]
White-bordered green diamond symbol used on LPG-powered vehicles in China
When LPG is used to fuelinternal combustion engines, it is often referred to asautogas or auto propane. In some countries, it has been used since the 1940s as a petrol alternative for spark ignition engines. In some countries, there are additives in the liquid that extend engine life and the ratio of butane to propane is kept quite precise in fuel LPG. Two recent studies have examined LPG-fuel-oil fuel mixes and found that smoke emissions and fuel consumption are reduced buthydrocarbon emissions are increased.[22][23] The studies were split on CO emissions, with one finding significant increases,[22] and the other finding slight increases at low engine load but a considerable decrease at high engine load.[23] Its advantage is that it is non-toxic, non-corrosive and free oftetraethyllead or any additives, and has a highoctane rating (102–108RON depending on local specifications). It burns more cleanly than petrol or fuel-oil and is especially free of theparticulates present in the latter.
LPG has a lower energy density per liter than either petrol or fuel-oil, so the equivalentfuel consumption is higher. Many governments impose less tax on LPG than on petrol or fuel-oil, which helps offset the greater consumption of LPG than of petrol or fuel-oil. However, in many European countries, this tax break is often compensated by a much higher annual tax on cars using LPG than on cars using petrol or fuel-oil. Propane is the third most widely used motor fuel in the world. 2013 estimates are that over 24.9 million vehicles are fueled by propane gas worldwide. Over 25 million tonnes (over 9 billion US gallons) are used annually as a vehicle fuel.
Not all automobile engines are suitable for use with LPG as a fuel. LPG provides less upper cylinder lubrication than petrol or diesel, so LPG-fueled engines are more prone to valve wear if they are not suitably modified. Many modern common rail diesel engines respond well to LPG use as a supplementary fuel. This is where LPG is used as fuel as well as diesel. Systems are now available that integrate with OEM engine management systems.
Conversion kits can switch a vehicle dedicated to gasoline to using a dual system, in which both gasoline and LPG are used in the same vehicle.
In 2020, BW LPG successfully retrofitted a Very Large Gas Carrier (VLGC) with LPG propulsion technology, pioneering LPG's application in large-scale maritime operations.[24] LPG's lowers emissions of carbon dioxide, sulfur oxides, nitrogen oxides, and particulate matter[25][26] align with stricter standards set by the International Maritime Organization (IMO), making LPG a viable transition option as the maritime industry transitions towards net zero carbon emissions.[27]
Such substitution is widely prohibited or discouraged in motor vehicle air conditioning systems, on the grounds that usingflammable hydrocarbons in systems originally designed to carry non-flammable refrigerant presents a significant risk of fire or explosion.[29][30]
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.[31][32] One particular test, conducted by a professor at theUniversity of New South Wales, unintentionally tested the worst-case scenario of a sudden and complete refrigerant expulsion into the passenger compartment followed by subsequent ignition. He and several others in the car sustained minor burns to their face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window. No one was seriously injured.[33]
Global LPG production reached over 292 million metric tons per year (Mt/a) in 2015, while global LPG consumption to over 284 Mt/a.[37] 62% of LPG is extracted fromnatural gas while the rest is produced by petroleum refineries fromcrude oil.[38] 44% of global consumption is in the domestic sector. The U.S. is the leading producer and exporter of LPG.[39]
Because of the natural gas and the oil-refining industry, Europe is almost self-sufficient in LPG. Europe's security of supply is further safeguarded by:
a wide range of sources, both inside and outside Europe;
a flexible supply chain via water, rail and road with numerous routes and entry points into Europe.
According to 2010–12 estimates,proven world reserves of natural gas, from which most LPG is derived, stand at 300 trillion cubic meters (10,600 trillion cubic feet). Production continues to grow at an average annual rate of 2.2%.
LPG is composed mainly of propane and butane, while natural gas is composed of the lightermethane andethane. LPG, vaporised and at atmospheric pressure, has a highercalorific value (46 MJ/m3 equivalent to 12.8 kWh/m3) thannatural gas (methane) (38 MJ/m3 equivalent to 10.6 kWh/m3), which means that LPG cannot 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 theWobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable.[40]
LPG-based SNG is used in emergency backup systems for many public, industrial and military installations, and many utilities use LPGpeak 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.
LPG-based SNG or natural gas with localized storage and piping distribution network to the households for catering to each cluster of 5000 domestic consumers can be planned under the initial phase of the city gas network system. This would eliminate the last mile LPG cylinders road transport which is a cause of traffic and safety hurdles in Indian cities. These localized natural gas networks are successfully operating in Japan with feasibility to get connected to wider networks in both villages and cities.
Commercially available LPG is currently derived mainly from fossil fuels. Burning LPG releasescarbon dioxide, agreenhouse gas. The reaction also produces somecarbon monoxide. LPG does, however, release lessCO 2 per unit of energy than does coal or oil, but more than natural gas. It emits 81% of theCO 2 perkWh produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid.[41] Being a mix of propane and butane, LPG emits less carbon perjoule than butane but more carbon per joule than propane.
As it is much less polluting than most traditional solid-fuel stoves, replacing cookstoves used in developing countries with LPG is one of the key strategies adopted to reducehousehold air pollution in the developing world.[43]
LPG Horton sphere tanks at aRepsol Butano facility in Gijón, Spain
In a refinery or gas plant, LPG must be stored inpressure vessels. These containers are either cylindrical and horizontal (sometimes referred to as bullet tanks) or spherical (of theHorton sphere type). Typically, these vessels are designed and manufactured according to some code. In the United States, this code is governed by theAmerican Society of Mechanical Engineers (ASME).
LPG containers have pressure relief valves, such that when subjected to exterior heating sources, they will vent LPGs to the atmosphere or aflare stack.
If a tank is subjected to a fire of sufficient duration and intensity, it can undergo aboiling liquid expanding vapor explosion (BLEVE). This is typically a concern for large refineries and petrochemical plants that maintain very large containers. In general, tanks are designed so that the product will vent faster than pressure can build to dangerous levels.
One remedy that is utilized in industrial settings is to equip such containers with a measure to provide afire-resistance rating. Large, spherical LPG containers may have up to a 15 cm steel wall thickness. They are equipped with an approved pressure reliefvalve. A large fire in the vicinity of the vessel will increase its temperature andpressure. The relief valve on the top is designed to vent off excess pressure in order to prevent the rupture of the container 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. Alternatively, if, due to continued venting, the liquid level drops below the area being heated, the tank structure can be overheated and subsequently weakened in that area. If either occurs, the container may rupture violently, launching pieces of the vessel at high velocity, while the released products can ignite as well, potentially causing catastrophic damage to anything nearby, including other containers.[44]
^abZhang, Chunhua; Bian, Yaozhang; Si, Lizeng; Liao, Junzhi; Odbileg, N (2005). "A study on an electronically controlled liquefied petroleum gas-diesel dual-fuel automobile".Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering.219 (2): 207.doi:10.1243/095440705X6470.S2CID109657186.
^abQi, D; Bian, Y; Ma, Z; Zhang, C; Liu, S (2007). "Combustion and exhaust emikon characteristics of a compression ignition engine using liquefied petroleum gas–fuel-oil blended fuel".Energy Conversion and Management.48 (2): 500.doi:10.1016/j.enconman.2006.06.013.
^Iemma, Morris; Lo Po', Faye (16 October 1997)."Motor Vehicle Hydrocarbons". Parliament of New South Wales. Archived fromthe original on 1 July 2009. Retrieved30 July 2009.
^Johnson, R. (2006). "The Effect of Pressure Relief Valve Blowdown and Fire Conditions on LPG Pressure Vessels".Journal of Pressure Vessel Technology.128 (3):467–473.doi:10.1115/1.2184608.
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