![13-08-09-hongkong-by-RalfR-106](https://upload.wikimedia.org/wikipedia/commons/a/a4/13-08-09-hongkong-by-RalfR-106.jpg)
Liquefied petroleum gas (LPG or LP gas) is a
fuel gas
Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources energy t ...
which contains a
flammable mixture of
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
gases, specifically
propane, propylene, butylene, isobutane and
n-butane
Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name bu ...
.
LPG is used as a
fuel gas
Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources energy t ...
in
heating appliances, cooking equipment, and vehicles. It is increasingly used as an
aerosol propellant and a
refrigerant, replacing
chlorofluorocarbon
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and prop ...
s in an effort to reduce damage to the
ozone layer. When specifically used as a vehicle fuel, it is often referred to as
autogas
Autogas or LPG is liquefied petroleum gas (LPG) used as a fuel in internal combustion engines in vehicles as well as in stationary applications such as generators. It is a mixture of propane and butane.
Autogas is widely used as a "green" ...
or even just as
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
.
Varieties of LPG that are bought and sold include mixes that are mostly propane (), mostly butane (), 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.
In the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, mainly two grades of LPG are sold: commercial propane and HD-5. These specifications are published by the Gas Processors Association (GPA)
and the American Society of Testing and Materials. Propane/butane blends are also listed in these specifications.
Propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...
,
butylene
Butene, also known as butylene, is an alkene with the formula . The word ''butene'' may refer to any of the individual compounds. They are colourless gases that are present in crude oil as a minor constituent in quantities that are too small for ...
s and various other hydrocarbons are usually also present in small concentrations such as , , and . HD-5 limits the amount of propylene that can be placed in LPG to 5% and is utilized as an autogas specification. A powerful
odorant
An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently vol ...
,
ethanethiol
Ethanethiol, commonly known as ethyl mercaptan, is an organosulfur compound with the formula CH3CH2SH. is a colorless liquid with a distinct odor. Abbreviated EtSH, it consists of an ethyl group (Et), CH3CH2, attached to a thiol group, SH. Its st ...
, is added so that leaks can be detected easily. The internationally recognized European Standard is EN 589. In the United States,
tetrahydrothiophene
Tetrahydrothiophene is an organosulfur compound with the formula (CH2)4S. The molecule consists of a five-membered saturated ring with four methylene groups and a sulfur atom. It is the saturated analog of thiophene. It is a volatile, colorles ...
(thiophane) or
amyl mercaptan are also approved odorants, although neither is currently being utilized.
LPG is prepared by
refining petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
or "wet"
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, and is almost entirely derived from
fossil fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
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 by
Walter O. Snelling
Walter Otheman Snelling (December 13, 1880September 10, 1965) was a chemist who contributed to the development of explosives, ordnance, and liquefied petroleum gas.
Early life and career
Walter Otheman Snelling was born in Washington, D.C. on De ...
, and the first commercial products appeared in 1912. It currently provides about 3% of all energy consumed, and burns relatively cleanly with no
soot
Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
and very few
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
emissions. As it is a gas, it does not pose ground or
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
hazards, but it can cause
air pollution
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different typ ...
. LPG has a typical specific
calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for
fuel oil and 43.5 MJ/kg for premium grade
petrol
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
(gasoline). However, its
energy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as its
relative density is lower (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L for
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
). 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 or
custody transfer
Custody Transfer in the oil and gas industry refers to the transactions involving transporting physical substance from one operator to another. This includes the transferring of raw and refined petroleum between tanks and railway tank cars; onto s ...
operations, 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, propylene, butene as well as acrylic acid.
As its boiling point is below room
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
, LPG will evaporate quickly at normal temperatures and
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
s and is usually supplied in pressurized
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
vessels. They are typically filled to 80–85% of their capacity to allow for
thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its
vapour pressure
Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase ...
, likewise varies depending on composition and temperature; for example, it is approximately for pure
butane at , and approximately for pure
propane at . LPG is heavier than
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
, unlike
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, and thus will flow along floors and tend to settle in low spots, such as
basements. There are two main dangers to this. The first is a possible
explosion if the mixture of LPG and air is within the
explosive limits
Mixtures of dispersed combustible materials (such as gaseous or vaporised fuels, and some dusts) and oxygen in the air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to a ...
and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration.
A full LPG cylinder contains 86% liquid; the
ullage
Ullage or headspace is the unfilled space in a container, particularly with a liquid.
Etymology
The word ''ullage'' comes from the Latin word ''oculus'', used by the Romans to refer to a barrel cork hole. This word was, in turn, taken in medieval ...
volume will contain vapour at a pressure that varies with temperature.
Uses
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 and water heating and is a particularly cost-effective and efficient way to heat off-grid homes.
Cooking
LPG is used for cooking in many countries for economic reasons, for convenience or because it is the preferred fuel source.
In India, nearly 8.9 million tons of LPG were consumed in the six months between April and September 2016 in the domestic sector, mainly for cooking. The number of domestic connections are 215 million (i.e., one connection for every six people) with a circulation of more than 350 million LPG cylinders. 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 the
middle class
The middle class refers to a class of people in the middle of a social hierarchy, often defined by occupation, income, education, or social status. The term has historically been associated with modernity, capitalism and political debate. Com ...
voting pattern.
LPG was once a standard cooking fuel in
Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
; however, the continued expansion of
''town 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 in
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
ian 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
Bolsa Família (, ''Family Allowance'') was a social welfare program of the Government of Brazil, part of the Fome Zero network of federal assistance programs. Bolsa Família provided financial aid to poor Brazilian families. In order to be el ...
"). Also, since 2005, the national oil company
Petrobras 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.
LPG is commonly used in
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
for domestic cooking and outdoor
grilling.
Rural heating
![Liquefied petroleum gas cylinders](https://upload.wikimedia.org/wikipedia/commons/2/22/Liquefied_petroleum_gas_cylinders.jpg)
Predominantly in Europe and rural parts of many countries, LPG can provide an alternative to
electric heating
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. ...
,
heating oil, or
kerosene
Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...
. LPG is most often used in areas that do not have direct access to piped
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
.
LPG can be used as a power source for
combined 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.
![Majuro Energy Company bottling LPG](https://upload.wikimedia.org/wikipedia/commons/0/04/Majuro_Energy_Company_bottling_LPG.png)
LPG can be stored in a variety of manners. LPG, as with other fossil fuels, can be combined with
renewable power sources to provide greater reliability while still achieving some reduction in CO
2 emissions. However, as opposed to
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
and
solar renewable energy sources, LPG can be used as a standalone energy source without the prohibitive expense of electrical
energy 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.
Motor fuel
![LPG logo China](https://upload.wikimedia.org/wikipedia/commons/9/95/LPG_logo_China.svg)
When LPG is used to fuel
internal combustion engines
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
, it is often referred to as
autogas
Autogas or LPG is liquefied petroleum gas (LPG) used as a fuel in internal combustion engines in vehicles as well as in stationary applications such as generators. It is a mixture of propane and butane.
Autogas is widely used as a "green" ...
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 but
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
emissions are increased.
The studies were split on CO emissions, with one finding significant increases,
and the other finding slight increases at low engine load but a considerable decrease at high engine load.
Its advantage is that it is non-toxic, non-corrosive and free of
tetraethyllead
Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It is a fuel additive, first being mixed with gasoline beginning in the 1920s as a patented octane rating booster that ...
or any additives, and has a high
octane rating (102–108 RON depending on local specifications). It burns more cleanly than petrol or fuel-oil and is especially free of the
particulate
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...
s present in the latter.
LPG has a lower energy density per liter than either petrol or fuel-oil, so the equivalent
fuel consumption
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
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.
Conversion to gasoline
LPG can be converted into
alkylate
An alkylation unit (alky) is one of the conversion processes used in petroleum refineries. It is used to convert isobutane and low-molecular-weight alkenes (primarily a mixture of propene and butene) into alkylate, a high octane gasoline componen ...
which is a premium
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
blending stock because it has exceptional anti-knock properties and gives clean burning.
Refrigeration
LPG is instrumental in providing
off-the-grid
Off-the-grid or off-grid is a characteristic of buildings and a lifestyle designed in an independent manner without reliance on one or more public utilities. The term "off-the-grid" traditionally refers to not being connected to the electrical gr ...
refrigeration, usually by means of a
gas absorption refrigerator
An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a fossil-fueled flame, waste heat from factories, or district heating systems) to provide the energy needed to drive the cooling process. The system uses t ...
.
Blended of pure, dry propane (refrigerant designator R-290) and
isobutane (R-600a) the blend "R-290a" has negligible
ozone depletion potential
The ozone depletion potential (ODP) of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane (R-11 or CFC-11) being fixed at an ODP of 1.0. Chlorodifluoromethane (R-22), for exampl ...
and very low
global warming potential
Global warming potential (GWP) is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (). GWP is 1 for . For other gases it depends on the gas and the time ...
and can serve as a functional replacement for
R-12,
R-22,
R-134a
1,1,1,2-Tetrafluoroethane (also known as norflurane (INN), R-134a, Freon 134a, Forane 134a, Genetron 134a, Green Gas, Florasol 134a, Suva 134a, or HFC-134a) is a hydrofluorocarbon (HFC) and haloalkane refrigerant with thermodynamic properties ...
and other
chlorofluorocarbon
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and prop ...
or
hydrofluorocarbon
Hydrofluorocarbons (HFCs) are man-made organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air condi ...
refrigerants in conventional stationary refrigeration and air conditioning systems.
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, conducted by a professor at the
University of New South Wales
The University of New South Wales (UNSW), also known as UNSW Sydney, is a public research university based in Sydney, New South Wales, Australia. It is one of the founding members of Group of Eight, a coalition of Australian research-intensiv ...
, 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.
Propellant
Global production
Global LPG production reached over 292 million metric tons per year (Mt/a) in 2015, while global LPG consumption to over 284 Mt/a. 62% of LPG is extracted from
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
while the rest is produced by petroleum refineries from
crude oil
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
. 44% of global consumption is in the domestic sector. The U.S. is the leading producer and exporter of LPG.
Security of supply
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%.
Comparison with natural gas
LPG is composed mainly of propane and butane, while natural gas is composed of the lighter methane and ethane. LPG, vaporised and at atmospheric pressure, has a higher
calorific value (46 MJ/m
3 equivalent to 12.8 kWh/m
3) than
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
(
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
) (38 MJ/m
3 equivalent to 10.6 kWh/m
3), 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 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
Load management, also known as demand-side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. This can be ach ...
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.
Environmental effects
Commercially available LPG is currently derived mainly from fossil fuels. Burning LPG releases
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, a
greenhouse gas. The reaction also produces some
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
. LPG does, however, release less per unit of energy than does coal or oil, but more than natural gas. It emits 81% of the per
kWh produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid. Being a mix of propane and butane, LPG emits less carbon per
joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...
than butane but more carbon per joule than propane.
LPG burns more cleanly than higher molecular weight
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s because it releases fewer
particulates
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The t ...
.
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 reduce
household air pollution
Household air pollution (HAP) is a significant form of indoor air pollution mostly relating to cooking and heating methods used in developing countries. Since much of the cooking is carried out with biomass fuel, in the form of wood, charcoal, ...
in the developing world.
Fire/explosion risk and mitigation
In a refinery or gas plant, LPG must be stored in
pressure vessels
A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.
Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...
. These containers are either cylindrical and horizontal or spherical. Typically, these vessels are designed and manufactured according to some code. In the United States, this code is governed by the
American 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 a
flare stack
A gas flare, alternatively known as a flare stack, flare boom, ground flare, or flare pit is a gas combustion device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites havi ...
.
If a tank is subjected to a fire of sufficient duration and intensity, it can undergo a boiling liquid expanding vapor explosion (
BLEVE
A boiling liquid expanding vapor explosion (BLEVE, ) is an explosion caused by the rupture of a vessel containing a pressurized liquid that has reached temperature above its boiling point. Because the boiling point of a liquid rises wi ...
). 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 a
fire-resistance rating
A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail other criteria, involving eviden ...
. Large, spherical LPG containers may have up to a 15 cm steel wall thickness. They are equipped with an approved pressure relief
valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
. A large fire in the vicinity of the vessel will increase its temperature and
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
. 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.
People can be exposed to LPG in the workplace by breathing it in, skin contact, and eye contact. The
Occupational Safety and Health Administration
The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...
(OSHA) has set the legal limit (
Permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupational ...
) for LPG exposure in the workplace as 1000 ppm (1800 mg/m
3) over an 8-hour workday. The
National Institute for Occupational Safety and Health
The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...
(NIOSH) has set a
recommended exposure limit
A recommended exposure limit (REL) is an occupational exposure limit that has been recommended by the United States National Institute for Occupational Safety and Health. The REL is a level that NIOSH believes would be protective of worker safet ...
(REL) of 1000 ppm (1800 mg/m
3) over an 8-hour workday. At levels of 2000 ppm, 10% of the lower explosive limit, LPG is considered
immediately dangerous to life and health
The term immediately dangerous to life or health (IDLH) is defined by the US National Institute for Occupational Safety and Health (NIOSH) as exposure to airborne contaminants that is "likely to cause death or immediate or delayed permanent advers ...
(due solely to safety considerations pertaining to risk of explosion).
See also
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Compressed natural gas
Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of , usually in cy ...
(CNG)
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Filling carousel
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Gasoline gallon equivalent
Gasoline gallon equivalent (GGE) or gasoline-equivalent gallon (GEG) is the amount of an alternative fuel it takes to equal the energy content of one liquid gallon of gasoline. GGE allows consumers to compare the energy content of competing fu ...
*
Industrial gas
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Intumescent
An intumescent is a substance that swells as a result of heat exposure, leading to an increase in volume and decrease in density. Intumescent materials are typically used in passive fire protection and require listing, approval, and compliance in ...
*
POL valve
A POL valve (originally for Prest-O-Lite) is a gas connection fitting used on Liquefied petroleum gas (LPG) cylinders.
The oldest standard for such connections, it was developed by the Prest-O-Lite company, hence the name. It is still the mos ...
References
http://www.ces.iisc.ernet.in/energy/paper/alternative/calorific.html
External links
Propane 101Explaining propane and LP Gas fundamentals
Centers for Disease Control and Prevention
Difference between CNG and LPG
{{DEFAULTSORT:Liquefied Petroleum Gas
Liquefied petroleum gas,
Petroleum production