Natural-gas processing

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Natural-gas_processing

A natural-gas processing plant in Aderklaa, Austria

Natural-gas processing is a range of industrial processes designed to purify raw natural gas by removing contaminants such as solids, water, carbon dioxide (CO₂), hydrogen sulfide (H₂S), mercury and higher molecular mass hydrocarbons (condensate) to produce pipeline quality dry natural gas for pipeline distribution and final use. Some of the substances which contaminate natural gas have economic value and are further processed or sold. Hydrocarbons that are liquid at ambient conditions: temperature and pressure (i.e., pentane and heavier) are called natural-gas condensate (sometimes also called natural gasoline or simply condensate).

Raw natural gas comes primarily from three types of wells: crude oil wells, gas wells, and condensate wells. Crude oil and natural gas are often found together in the same reservoir. Natural gas produced in wells with crude oil is generally classified as associated-dissolved gas as the gas had been associated with or dissolved in crude oil. Natural gas production not associated with crude oil is classified as “non-associated.” In 2009, 89 percent of U.S. wellhead production of natural gas was non-associated. Non-associated gas wells producing a dry gas in terms of condensate and water can send the dry gas directly to a pipeline or gas plant without undergoing any separation processing allowing immediate use.

Natural-gas processing begins underground or at the well-head. In a crude oil well, natural gas processing begins as the fluid loses pressure and flows through the reservoir rocks until it reaches the well tubing. In other wells, processing begins at the wellhead which extracts the composition of natural gas according to the type, depth, and location of the underground deposit and the geology of the area.

Natural gas when relatively free of hydrogen sulfide is called sweet gas; natural gas that contains elevated hydrogen sulfide levels is called sour gas; natural gas, or any other gas mixture, containing significant quantities of hydrogen sulfide or carbon dioxide or similar acidic gases, is called acid gas.

Types of raw-natural-gas wells

• Crude oil wells: Natural gas that comes from crude oil wells is typically called associated gas. This gas could exist as a separate gas cap above the crude oil in the underground reservoir or could be dissolved in the crude oil, ultimately coming out of solution as the pressure is reduced during production. Condensate produced from oil wells is often referred to as lease condensate.
• Dry gas wells: These wells typically produce only raw natural gas that contains no condensate with little to no crude oil and are called non-associated gas. Condensate from dry gas is extracted at gas processing plants and is often called plant condensate.
• Condensate wells: These wells typically produce raw natural gas along with natural gas liquid with little to no crude oil and are called non-associated gas. Such raw natural gas is often referred to as wet gas.
• Coal seam wells: These wells typically produce raw natural gas from methane deposits in the pores of coal seams, often existing underground in a more concentrated state of adsorption onto the surface of the coal itself. Such gas is referred to as coalbed gas or coalbed methane (coal seam gas in Australia). Coalbed gas has become an important source of energy in recent decades.

Contaminants in raw natural gas

See also: Natural-gas condensate

Raw natural gas typically consists primarily of methane (CH₄) and ethane (C₂H₆), the shortest and lightest hydrocarbon molecules. It often also contains varying amounts of:

• Heavier gaseous hydrocarbons: propane (C₃H₈), normal butane (n-C₄H₁₀), isobutane (i-C₄H₁₀) and pentanes. All of these are collectively referred to as Natural Gas Liquids or NGL and can be processed into finished by-products.
• Liquid hydrocarbons (also referred to as casinghead gasoline or natural gasoline) and/or crude oil.
• Acid gases: carbon dioxide (CO₂), hydrogen sulfide (H₂S) and mercaptans such as methanethiol (CH₃SH) and ethanethiol (C₂H₅SH).
• Other gases: nitrogen (N₂) and helium (He).
• Water: water vapor and liquid water. Also dissolved salts and dissolved gases (acids).
• Mercury: minute amounts of mercury primarily in elemental form, but chlorides and other species are possibly present.
• Naturally occurring radioactive material (NORM): natural gas may contain radon, and the produced water may contain dissolved traces of radium, which can accumulate within piping and processing equipment; rendering piping and equipment radioactive over time.

Natural gas quality standards

Raw natural gas must be purified to meet the quality standards specified by the major pipeline transmission and distribution companies. Those quality standards vary from pipeline to pipeline and are usually a function of a pipeline system's design and the markets that it serves. In general, the standards specify that the natural gas:

• Be within a specific range of heating value (caloric value). For example, in the United States, it should be about 1035 ± 5% BTU per cubic foot of gas at 1 atmosphere and 60 °F (41 MJ ± 5% per cubic metre of gas at 1 atmosphere and 15.6 °C). In the United Kingdom the gross calorific value must be in the range 37.0 – 44.5 MJ/m³ for entry into the National Transmission System (NTS).
• Be delivered at or above a specified hydrocarbon dew point temperature (below which some of the hydrocarbons in the gas might condense at pipeline pressure forming liquid slugs that could damage the pipeline.) Hydrocarbon dew-point adjustment reduces the concentration of heavy hydrocarbons so no condensation occurs during the ensuing transport in the pipelines. In the UK the hydrocarbon dew point is defined as <-2 °C for entry into the NTS. The hydrocarbon dewpoint changes with the prevailing ambient temperature, the seasonal variation is:

Seasonal variation of hydrocarbon dewpoint

Hydrocarbon dewpoint	30 °F (–1.1 °C)	35 °F (1.7 °C)	40 °F (4.4 °C)	45 °F (7.2 °C)	50 °F (10 °C)
Months	December January February March	April November	May October	June September	July August

The natural gas should:

• Be free of particulate solids and liquid water to prevent erosion, corrosion or other damage to the pipeline.
• Be dehydrated of water vapor sufficiently to prevent the formation of methane hydrates within the gas processing plant or subsequently within the sales gas transmission pipeline. A typical water content specification in the U.S. is that gas must contain no more than seven pounds of water per million standard cubic feet of gas. In the UK this is defined as <-10 °C @ 85barg for entry into the NTS.
• Contain no more than trace amounts of components such as hydrogen sulfide, carbon dioxide, mercaptans, and nitrogen. The most common specification for hydrogen sulfide content is 0.25 grain H₂S per 100 cubic feet of gas, or approximately 4 ppm. Specifications for CO₂ typically limit the content to no more than two or three percent. In the UK hydrogen sulfide is specified ≤5 mg/m³ and total sulfur as ≤50 mg/m³, carbon dioxide as ≤2.0% (molar), and nitrogen as ≤5.0% (molar) for entry into the NTS.
• Maintain mercury at less than detectable limits (approximately 0.001 ppb by volume) primarily to avoid damaging equipment in the gas processing plant or the pipeline transmission system from mercury amalgamation and embrittlement of aluminum and other metals.

Description of a natural-gas processing plant

There are a variety of ways in which to configure the various unit processes used in the treatment of raw natural gas. The block flow diagram below is a generalized, typical configuration for the processing of raw natural gas from non-associated gas wells showing how raw natural gas is processed into sales gas piped to the end user markets and various byproducts:

• Natural-gas condensate
• Sulfur
• Ethane
• Natural gas liquids (NGL): propane, butanes and C₅+ (which is the commonly used term for pentanes plus higher molecular weight hydrocarbons)

Raw natural gas is commonly collected from a group of adjacent wells and is first processed in a separator vessels at that collection point for removal of free liquid water and natural gas condensate. The condensate is usually then transported to an oil refinery and the water is treated and disposed of as wastewater.

The raw gas is then piped to a gas processing plant where the initial purification is usually the removal of acid gases (hydrogen sulfide and carbon dioxide). There are several processes available for that purpose as shown in the flow diagram, but amine treating is the process that was historically used. However, due to a range of performance and environmental constraints of the amine process, a newer technology based on the use of polymeric membranes to separate the carbon dioxide and hydrogen sulfide from the natural gas stream has gained increasing acceptance. Membranes are attractive since no reagents are consumed.

The acid gases, if present, are removed by membrane or amine treating and can then be routed into a sulfur recovery unit which converts the hydrogen sulfide in the acid gas into either elemental sulfur or sulfuric acid. Of the processes available for these conversions, the Claus process is by far the most well known for recovering elemental sulfur, whereas the conventional Contact process and the WSA (Wet sulfuric acid process) are the most used technologies for recovering sulfuric acid. Smaller quantities of acid gas may be disposed of by flaring.

The residual gas from the Claus process is commonly called tail gas and that gas is then processed in a tail gas treating unit (TGTU) to recover and recycle residual sulfur-containing compounds back into the Claus unit. Again, as shown in the flow diagram, there are a number of processes available for treating the Claus unit tail gas and for that purpose a WSA process is also very suitable since it can work autothermally on tail gases.

The next step in the gas processing plant is to remove water vapor from the gas using either the regenerable absorption in liquid triethylene glycol (TEG), commonly referred to as glycol dehydration, deliquescent chloride desiccants, and or a Pressure Swing Adsorption (PSA) unit which is regenerable adsorption using a solid adsorbent. Other newer processes like membranes may also be considered.

Mercury is then removed by using adsorption processes (as shown in the flow diagram) such as activated carbon or regenerable molecular sieves.

Although not common, nitrogen is sometimes removed and rejected using one of the three processes indicated on the flow diagram:

• Cryogenic process (Nitrogen Rejection Unit), using low temperature distillation. This process can be modified to also recover helium, if desired (see also industrial gas).
• Absorption process, using lean oil or a special solvent as the absorbent.
• Adsorption process, using activated carbon or molecular sieves as the adsorbent. This process may have limited applicability because it is said to incur the loss of butanes and heavier hydrocarbons.

NGL fractionation train

The NGL fractionation process treats offgas from the separators at an oil terminal or the overhead fraction from a crude distillation column in a refinery. Fractionation aims to produce useful products including natural gas suitable for piping to industrial and domestic consumers; liquefied petroleum gases (Propane and Butane) for sale; and gasoline feedstock for liquid fuel blending. The recovered NGL stream is processed through a fractionation train consisting of up to five distillation towers in series: a demethanizer, a deethanizer, a depropanizer, a debutanizer and a butane splitter. The fractionation train typically uses a cryogenic low temperature distillation process involving expansion of the recovered NGL through a turbo-expander followed by distillation in a demethanizing fractionating column. Some gas processing plants use lean oil absorption process rather than the cryogenic turbo-expander process.

The gaseous feed to the NGL fractionation plant is typically compressed to about 60 barg and 37 °C. The feed is cooled to -22 °C, by exchange with the demethanizer overhead product and by a refrigeration system and is split into three streams:

• condensed liquid passes through a Joule-Thomson valve reducing the pressure to 20 bar and enters the demethanizer as the lower feed at -44.7 °C.
• some of the vapour is routed through a turbo-expander and enters the demethanizer as the upper feed at -64 °C.
• the remaining vapor is chilled by the demethanizer overhead product and Joule-Thomson cooling (through a valve) and enters the column as reflux at -96 °C.

The overhead product is mainly methane at 20 bar and -98 °C. This is heated and compressed to yield a sales gas at 20 bar and 40 °C. The bottom product is NGL at 20 barg which is fed to the deethanizer.  

The overhead product from the deethanizer is ethane and the bottoms are fed to the depropanizer. The overhead product from the depropanizer is propane and the bottoms are fed to the debutanizer. The overhead product from the debutanizer is a mixture of normal and iso-butane, and the bottoms product is a C₅+ gasoline mixture.

The operating conditions of the vessels in the NGL fractionation train are typically as follows.

NGL column operating conditions

	Demethanizer	Deethanizer	Depropanizer	Debutanizer	Butane Splitter
Feed pressure	60 barg	30 barg
Feed temperature	37 °C	25 °C	37 °C	125 °C	59 °C
Column operating pressure	20 barg	26-30 barg	10-16.2 barg	3.8-17 barg	4.9-7 barg
Overhead product temperature	-98°C		50 °C	59 °C	49 °C
Bottom product temperature	12 °C	37 °C	125 °C	118 °C	67 °C
Overhead product	Methane (natural gas)	Ethane	Propane	Butane	Isobutane
Bottom product	Natural gas liquids	(Depropanizer feed)	(Debutanizer feed)	Gasoline	Normal Butane

A typical composition of the feed and product is as follows.

Stream composition, % volume

Component	Feed	NGL	Ethane	Propane	Isobutane	n-Butane	Gasoline
Methane	89.4	0.5	1.36
Ethane	4.9	37.0	95.14	7.32
Propane	2.2	26.0	3.5	90.18	2.0
Isobutane	1.3	7.2		2.5	96.0	4.5
n-Butane	2.2	14.8			2.0	95.0	3.0
Isopentane		5.0					33.13
n-Pentane		3.5				0.5	23.52
n-Hexane		4.0					26.9
n-Heptane		2.0					13.45
Total	100	100	100	100	100	100	100

Sweetening Units

The recovered streams of propane, butanes and C₅+ may be "sweetened" in a Merox process unit to convert undesirable mercaptans into disulfides and, along with the recovered ethane, are the final NGL by-products from the gas processing plant. Currently, most cryogenic plants do not include fractionation for economic reasons, and the NGL stream is instead transported as a mixed product to standalone fractionation complexes located near refineries or chemical plants that use the components for feedstock. In case laying pipeline is not possible for geographical reason, or the distance between source and consumer exceed 3000 km, natural gas is then transported by ship as LNG (liquefied natural gas) and again converted into its gaseous state in the vicinity of the consumer.

Products

The residue gas from the NGL recovery section is the final, purified sales gas which is pipelined to the end-user markets. Rules and agreements are made between buyer and seller regarding the quality of the gas. These usually specify the maximum allowable concentration of CO₂, H₂S and H₂O as well as requiring the gas to be commercially free from objectionable odours and materials, and dust or other solid or liquid matter, waxes, gums and gum forming constituents, which might damage or adversely affect operation of the buyers equipment. When an upset occurs on the treatment plant buyers can usually refuse to accept the gas, lower the flow rate or re-negotiate the price.

Helium recovery

If the gas has significant helium content, the helium may be recovered by fractional distillation. Natural gas may contain as much as 7% helium, and is the commercial source of the noble gas. For instance, the Hugoton Gas Field in Kansas and Oklahoma in the United States contains concentrations of helium from 0.3% to 1.9%, which is separated out as a valuable byproduct.

Propane

 

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Propane 

Propane

Names
Preferred IUPAC name Propane
Systematic IUPAC name Tricarbane (never recommended)
Identifiers
CAS Number	74-98-6
3D model (JSmol)	Interactive image
Beilstein Reference	1730718
ChEBI	CHEBI:32879
ChEMBL	ChEMBL135416
ChemSpider	6094
ECHA InfoCard	100.000.753
EC Number	200-827-9
E number	E944
Gmelin Reference	25044
KEGG	D05625
PubChem CID	6334
RTECS number	TX2275000
UNII	T75W9911L6
UN number	1978
CompTox Dashboard (EPA)	DTXSID5026386

SMILES
Properties[3]
Chemical formula	C3H8
Molar mass	44.097 g·mol−1
Appearance	Colorless gas
Odor	Odorless
Density	2.0098 kg/m3 (at 0 °C, 101.3 kPa)
Melting point	−187.7 °C; −305.8 °F; 85.5 K
Boiling point	−42.25 to −42.04 °C; −44.05 to −43.67 °F; 230.90 to 231.11 K
Solubility in water	47 mg⋅L−1 (at 0 °C)
log P	2.236
Vapor pressure	853.16 kPa (at 21.1 °C (70.0 °F))
Henry's law constant (kH)	15 nmol⋅Pa−1⋅kg−1
Conjugate acid	Propanium
Magnetic susceptibility (χ)	−40.5 × 10−6 cm3/mol
Dipole moment	0.083 D
Thermochemistry
Heat capacity (C)	73.60 J⋅K−1⋅mol−1
Std enthalpy of formation (ΔfH⦵298)	−105.2–104.2 kJ⋅mol−1
Std enthalpy of combustion (ΔcH⦵298)	−2.2197–2.2187 MJ⋅mol−1
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220
Precautionary statements	P210
NFPA 704 (fire diamond)	2 4 0
Flash point	−104 °C (−155 °F; 169 K)
Autoignition temperature	470 °C (878 °F; 743 K)
Explosive limits	2.37–9.5%
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1,000 ppm (1,800 mg/m3)
REL (Recommended)	TWA 1,000 ppm (1,800 mg/m3)
IDLH (Immediate danger)	2,100 ppm
Related compounds
Related alkanes	ethane butane isobutane
Related compounds	propene allene cyclopropane

A 20 lb (9.1 kg) steel propane cylinder. This cylinder is fitted with an overfill prevention device (OPD) valve, as evidenced by the trilobular handwheel.

Propane (/ˈproʊpeɪn/) is a three-carbon alkane with the molecular formula C₃H₈. It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel in domestic and industrial applications and in low-emissions public transportation. Discovered in 1857 by the French chemist Marcellin Berthelot, it became commercially available in the US by 1911. Propane is one of a group of liquefied petroleum gases (LP gases). The others include propylene, butane, butylene, butadiene, isobutylene, and mixtures thereof. Propane has lower volumetric energy density, but higher gravimetric energy density and burns more cleanly than gasoline and coal.

Propane gas has become a popular choice for barbecues and portable stoves because its low −42 °C boiling point makes it vaporise inside pressurised liquid containers (it exists in two phases, vapor above liquid). It retains its ability to vaporise even in cold weather, making it better-suited for outdoor use in cold climates than alternatives with higher boiling points like butane. Propane powers buses, forklifts, automobiles, outboard boat motors, and ice resurfacing machines, and is used for heat and cooking in recreational vehicles and campers.

History

Propane was discovered by the French chemist Marcellin Berthelot in 1857. It was found dissolved in Pennsylvanian light crude oil by Edmund Ronalds in 1864. Walter O. Snelling of the U.S. Bureau of Mines highlighted it as a volatile component in gasoline in 1910, which marked the "birth of the propane industry" in the United States. 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, 1912, The New York Times reported on Snelling's work with liquefied gas, saying "a steel bottle will carry enough gas to light an ordinary home for three weeks".

It was during this time that Snelling—in cooperation with Frank P. Peterson, Chester Kerr, and Arthur Kerr—developed ways to liquefy the LP gases during the refining of gasoline. Together, they established American Gasol Co., the first commercial marketer of propane. 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 developed by Frank Peterson and its patent was granted on July 2, 1912.

The 1920s saw increased production of LP gases, with the first year of recorded production totaling 223,000 US gallons (840 m³) in 1922. In 1927, annual marketed LP gas production reached 1 million US gallons (3,800 m³), and by 1935, the annual sales of LP gas had reached 56 million US gallons (210,000 m³). 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 US gallons (26,000,000 m³) annually. In 2004, it was reported to be a growing $8-billion to $10-billion industry with over 15 billion US gallons (57,000,000 m³) of propane being used annually in the U.S.

During the COVID-19 pandemic, propane shortages were reported in the United States due to increased demand.

Etymology

The "prop-" root found in "propane" and names of other compounds with three-carbon chains was derived from "propionic acid", which in turn was named after the Greek words protos (meaning first) and pion (fat), as it was the "first" member of the series of fatty acids.

Properties and reactions

Pyrometry of a propane flame using thin-filament velocimetry. The hottest parts of the flame are in a hollow cone-shaped area near its base and pointing upward.

  >1,750 K (1,480 °C)

  1,700 K (1,430 °C)

  1,600 K (1,330 °C)

  1,350 K (1,080 °C)

  1,100 K (830 °C)

  875 K (602 °C)

  750 K (477 °C)

Propane is a colorless, odorless gas. Ethyl mercaptan is added as a safety precaution as an odorant, and is commonly called a "rotten egg" smell. At normal pressure it liquifies below its boiling point at −42 °C and solidifies below its melting point at −187.7 °C. Propane crystallizes in the space group P2₁/n. The low space-filling of 58.5% (at 90 K), due to the bad stacking properties of the molecule, is the reason for the particularly low melting point.

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.

$${\displaystyle {\text{C}}_3^{}{\text{H}}_8^{}+5{\text{O}}_2^{}⟶3{\text{CO}}_2^{}+4{\text{H}}_2^{}\text{O}+\text{heat}}$$

When insufficient oxygen is present for complete combustion, carbon monoxide, soot (carbon), or both, are formed as well:

$${\displaystyle {\text{C}}_3^{}{\text{H}}_8^{}+\frac{9}{2}{\text{O}}_2^{}⟶2{\text{CO}}_2^{}+\text{CO}+4{\text{H}}_2^{}\text{O}+\text{heat}}$$

$${\displaystyle {\text{C}}_3^{}{\text{H}}_8^{}+2{\text{O}}_2^{}⟶3\text{C}+4{\text{H}}_2^{}\text{O}+\text{heat}}$$

The complete combustion of propane produces about 50 MJ/kg of heat.

Propane combustion is much cleaner than that of coal or unleaded gasoline. Propane's per-BTU production of CO₂ is almost as low as that of natural gas. Propane burns hotter than home heating oil or diesel fuel because of the very high hydrogen content. The presence of C–C bonds, plus the multiple bonds of propylene and butylene, produce organic exhausts besides carbon dioxide and water vapor during typical combustion. These bonds also cause propane to burn with a visible flame.

Energy content

The enthalpy of combustion of propane gas where all products return to standard state, for example where water returns to its liquid state at standard temperature (known as higher heating value), is (2,219.2 ± 0.5) kJ/mol, or (50.33 ± 0.01) MJ/kg.

The enthalpy of combustion of propane gas where products do not return to standard state, for example where the hot gases including water vapor exit a chimney, (known as lower heating value) is −2043.455 kJ/mol. The lower heat value is the amount of heat available from burning the substance where the combustion products are vented to the atmosphere; for example, the heat from a fireplace when the flue is open.

Density

The density of propane gas at 25 °C (77 °F) is 1.808 kg/m³, about 1.5× the density of air at the same temperature. The density of liquid propane at 25 °C (77 °F) is 0.493 g/cm³, which is equivalent to 4.11 pounds per U.S. liquid gallon or 493 g/L. Propane expands at 1.5% per 10 °F. Thus, liquid propane has a density of approximately 4.2 pounds per gallon (504 g/L) at 60 °F (15.6 °C).

As the density of propane changes with temperature, this fact must be considered every time when the application is connected with safety or custody transfer operations.

Temperature–density curve for liquid/vapor propane

Uses

Portable stoves

Propane is a popular choice for barbecues and portable stoves because the low boiling point of −42 °C (−44 °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.

Refrigerant

Blends of pure, dry "isopropane" (R-290a) (isobutane/propane mixtures) and isobutane (R-600a) can be used as the circulating refrigerant in suitably constructed compressor-based refrigeration. Compared to fluorocarbons, propane has a negligible ozone depletion potential and very low global warming potential (having a GWP value of 0.072, 13.9 times lower than the GWP of carbon dioxide) 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. Because its global warming effect is far less than current refrigerants, propane was chosen as one of five replacement refrigerants approved by the EPA in 2015, for use in systems specially designed to handle its flammability.

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.

Propane is also instrumental in providing off-the-grid refrigeration, as the energy source for a gas absorption refrigerator and is commonly used for camping and recreational vehicles.

It has also been proposed to use propane as a refrigerant in heat pumps.

Domestic and industrial fuel

Domestic spherical steel pressure vessel for propane storage.

Since it can be transported easily, it is a popular fuel for home heat and backup electrical generation in sparsely populated areas that do not have natural gas pipelines. In June 2023, Stanford researchers found propane combustion emitted detectable and repeatable levels of benzene that in some homes raised indoor benzene concentrations above well-established health benchmarks. The research also shows that gas and propane fuels appear to be the dominant source of benzene produced by cooking.

In rural areas of North America, as well as northern Australia, propane is used to heat livestock facilities, in 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 refilled by a propane-delivery truck. As of 2014, 6.2 million American households use propane as their primary heating fuel.

In North America, local delivery trucks with an average cylinder size of 3,000 US gallons (11 m³), fill up large cylinders that are permanently installed on the property, or other service trucks exchange empty cylinders of propane with filled cylinders. Large tractor-trailer trucks, with an average cylinder size of 10,000 US gallons (38 m³), transport propane from the pipeline or refinery to the local bulk plant. The bobtail tank truck is not unique to the North American market, though the practice is not as common elsewhere, and the vehicles are generally called tankers. In many countries, propane is delivered to end-users via small or medium-sized individual cylinders, while empty cylinders are removed for refilling at a central location.

There are also community propane systems, with a central cylinder feeding individual homes.

Motor fuel

Main article: Autogas

In the U.S., over 190,000 on-road vehicles use propane, and over 450,000 forklifts use it for power. It is the third most popular vehicle fuel in the world, behind gasoline and diesel fuel. In other parts of the world, propane used in vehicles is known as autogas. In 2007, approximately 13 million vehicles worldwide use autogas.

The advantage of propane in cars is its liquid state at a moderate pressure. This allows fast refill times, affordable fuel cylinder construction, and price ranges typically just over half that of 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 relatively low-cost in North America. The octane rating of propane is relatively high at 110. In the United States the propane fueling infrastructure is the most developed of all alternative vehicle fuels. 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. A further saving for propane fuel vehicle operators, especially in fleets, is that theft is much more difficult than with gasoline or diesel fuels.

Propane is also used as fuel for small engines, especially those used indoors or in areas with insufficient fresh air and ventilation to carry away the more toxic exhaust of an engine running on gasoline or diesel fuel. More recently, there have been lawn-care products like string trimmers, lawn mowers and leaf blowers intended for outdoor use, but fueled by propane in order to reduce air pollution.

Many heavy-duty highway trucks use propane as a boost, where it is added through the turbocharger, to mix with diesel fuel droplets. Propane droplets' very high hydrogen content helps the diesel fuel to burn hotter and therefore more completely. This provides more torque, more horsepower, and a cleaner exhaust for the trucks. It is normal for a 7-liter medium-duty diesel truck engine to increase fuel economy by 20 to 33 percent when a propane boost system is used. It is cheaper because propane is much cheaper than diesel fuel. The longer distance a cross-country trucker can travel on a full load of combined diesel and propane fuel means they can maintain federal hours of work rules with two fewer fuel stops in a cross-country trip. Truckers, tractor pulling competitions, and farmers have been using a propane boost system for over forty years in North America.

Other uses

• Propane is the primary flammable gas in blowtorches for soldering.
• Propane is used in oxy-fuel welding and cutting. Propane does not burn as hot as acetylene in its inner cone, and so it is rarely used for welding. Propane, however, has a very high number of BTUs per cubic foot in its outer cone, and so with the right torch (injector style) it can make a faster and cleaner cut than acetylene, and is much more useful for heating and bending than acetylene.
• Propane is used as a feedstock for the production of base petrochemicals in steam cracking.
• Propane is the primary fuel for hot-air balloons.
• It is used in semiconductor manufacture to deposit silicon carbide.
• Propane is commonly used in theme parks and in movie production as an inexpensive, high-energy fuel for explosions and other special effects.
• Propane is used as a propellant, relying on the expansion of the gas to fire the projectile. It does not ignite the gas. The use of a liquefied gas gives more shots per cylinder, compared to a compressed gas.
• Propane is also used as a cooking fuel.
• Propane is used as a propellant for many household aerosol sprays, including shaving creams and air fresheners.
• Propane is a promising feedstock for the production of propylene.
• Liquified propane is used in the extraction of animal fats and vegetable oils.

Purity

The North American standard grade of automotive-use propane is rated HD-5 (Heavy Duty 5%). HD-5 grade has a maximum of 5 percent butane, but propane sold in Europe has a maximum allowable amount of butane of 30 percent, meaning it is not the same fuel as HD-5. The LPG used as auto fuel and cooking gas in Asia and Australia also has very high butane content.

Propylene (also called propene) can be a contaminant of commercial propane. Propane containing too much propene is not suited for most vehicle fuels. HD-5 is a specification that establishes a maximum concentration of 5% propene in propane. Propane and other LP gas specifications are established in ASTM D-1835. All propane fuels include an odorant, almost always ethanethiol, so that the gas can be smelled easily in case of a leak. Propane as HD-5 was originally intended for use as vehicle fuel. HD-5 is currently being used in all propane applications.

Typically in the United States and Canada, LPG is primarily propane (at least 90%), while the rest is mostly ethane, propylene, butane, and odorants including ethyl mercaptan. This is the HD-5 standard, (maximum allowable propylene content, and no more than 5% butanes and ethane) defined by the American Society for Testing and Materials by its Standard 1835 for internal combustion engines. Not all products labeled "LPG" conform to this standard, however. In Mexico, for example, gas labeled "LPG" may consist of 60% propane and 40% butane. "The exact proportion of this combination varies by country, depending on international prices, on the availability of components and, especially, on the climatic conditions that favor LPG with higher butane content in warmer regions and propane in cold areas".

Comparison with natural gas

Propane is bought and stored in a liquid form, LPG. It can easily be stored in a relatively small space.

By comparison, compressed natural gas (CNG) cannot be liquefied by compression at normal temperatures, as these are well above its critical temperature. As a gas, very high pressure is required to store useful quantities. This poses the hazard that, in an accident, just as with any compressed gas cylinder (such as a CO₂ cylinder used for a soda concession) a CNG cylinder may burst with great force, or leak rapidly enough to become a self-propelled missile. Therefore, CNG is much less efficient to store than propane, due to the large cylinder volume required. An alternative means of storing natural gas is as a cryogenic liquid in an insulated container as liquefied natural gas (LNG). This form of storage is at low pressure and is around 3.5 times as efficient as storing it as CNG.

Unlike propane, if a spill occurs, CNG will evaporate and dissipate because it is lighter than air.

Propane is much more commonly used to fuel vehicles than is natural gas, because that equipment costs less. Propane requires just 1,220 kilopascals (177 psi) of pressure to keep it liquid at 37.8 °C (100 °F).

Hazards

Propane is a simple asphyxiant. Unlike natural gas, it is denser than air. It may accumulate in low spaces and near the floor. When abused as an inhalant, it may cause hypoxia (lack of oxygen), pneumonia, cardiac failure or cardiac arrest. Propane has low toxicity since it is not readily absorbed and is not biologically active. Commonly stored under pressure at room temperature, propane and its mixtures will flash evaporate at atmospheric pressure and cool well below the freezing point of water. The cold gas, which appears white due to moisture condensing from the air, may cause frostbite.

Propane is denser than air. If a leak in a propane fuel system occurs, the vaporized 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. This property makes propane generally unsuitable as a fuel for boats. In 2007, a heavily investigated vapor-related explosion occurred in Ghent, West Virginia, U.S., killing four people and completely destroying the Little General convenience store on Flat Top Road, causing several injuries.

Another hazard associated with propane storage and transport is known as a BLEVE or boiling liquid expanding vapor explosion. The Kingman Explosion involved a railroad tank car in Kingman, Arizona, U.S., in 1973 during a propane transfer. The fire and subsequent explosions resulted in twelve fatalities and numerous injuries.

Production

Propane is produced as a by-product 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 cracking petroleum into gasoline or heating oil.

The supply of propane cannot easily be adjusted to meet 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 separated from the crude oil, North American propane is stored in huge salt caverns. Examples of these are Fort Saskatchewan, Alberta; Mont Belvieu, Texas; and Conway, Kansas. These salt caverns can store 80,000,000 barrels (13,000,000 m³) of propane.

Retail cost

United States

As of October 2013, the retail cost of propane was approximately $2.37 per gallon, or roughly $25.95 per 1 million BTUs. This means that filling a 500-gallon propane tank, which is what households that use propane as their main source of energy usually require, cost $948 (80% of 500 gallons or 400 gallons), a 7.5% increase on the 2012–2013 winter season average US price. However, propane costs per gallon change significantly from one state to another: the Energy Information Administration (EIA) quotes a $2.995 per gallon average on the East Coast for October 2013, while the figure for the Midwest was $1.860 for the same period.

As of December 2015 the propane retail cost was approximately $1.97 per gallon. This means that filling a 500-gallon propane tank to 80% capacity cost $788, a 16.9% decrease or $160 less from the November 2013 quote in this section. Similar regional differences in prices are present with the December 2015 EIA figure for the East Coast at $2.67 per gallon and the Midwest at $1.43 per gallon.

As of August 2018 the average US propane retail cost was approximately $2.48 per gallon. The wholesale price of propane in the U.S. always drops in the summer as most homes do not require it for home heating. The wholesale price of propane in the summer of 2018 was between 86 cents to 96 cents per U.S. gallon, based on a truckload or railway car load. The price for home heating was exactly double that price; at 95 cents per gallon wholesale, a home-delivered price was $1.90 per gallon if ordered 500 gallons at a time. Prices in the Midwest are always cheaper than California. Prices for home delivery always go up near the end of August or the first few days of September when people start ordering their home tanks to be filled.

Radium and radon in the environment

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Radium_and_radon_in_the_environment 

Predicted fraction of U.S. homes have radon concentrations exceeding the EPA's recommended action level of 4 pCi/L

Radium and radon are important contributors to environmental radioactivity. Radon occurs naturally as a result of decay of radioactive elements in soil and it can accumulate in houses built on areas where such decay occurs. Radon is a major cause of cancer; it is estimated to contribute to ~2% of all cancer related deaths in Europe.

Radium, like radon, is radioactive and is found in small quantities in nature and is hazardous to life if radiation exceeds 20-50 mSv/year. Radium is a decay product of uranium and thorium. Radium may also be released into the environment by human activity, for example, in improperly discarded products painted with radioluminescent paint.

Radium

In the oil and gas industries

Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be very radium rich. The water inside an oil field is often very rich in strontium, barium and radium while seawater is very rich in sulfate so if water from an oil well is discharged into the sea or mixed with seawater the radium is likely to be brought out of solution by the barium/strontium sulfate which acts as a carrier precipitate.

Radioluminescent (glow in the dark) products

Local contamination from radium-based radioluminescent paints having been improperly disposed of is not unknown.

In radioactive quackery

Eben Byers was a wealthy American socialite whose death in 1932 from using a radioactive quackery product called Radithor is a prominent example of a death caused by radium. Radithor contained ~1 μCi (40 kBq) of ²²⁶Ra and 1 μCi of ²²⁸Ra per bottle. Radithor was taken by mouth and radium, being a calcium mimic, has a very long biological halflife in bone.

Radon

Radon in air forms a part of the background radiation, which can be observed in a cloud chamber

Most of the dose is due to the decay of the polonium (²¹⁸Po) and lead (²¹⁴Pb) daughters of ²²²Rn. By controlling exposure to the daughters the radioactive dose to the skin and lungs can be reduced by at least 90%. This can be done by wearing a dust mask, and wearing a suit to cover the entire body. Note that exposure to smoke at the same time as radon and radon daughters will increase the harmful effect of the radon. In uranium miners radon has been found to be more carcinogenic in smokers than in non-smokers.

The radium or uranium series.

Occurrence

Radon concentration in open air varies between 1 and 100 Bq m⁻³. Radon can be found in some spring waters and hot springs. The towns of Misasa, Japan, and Bad Kreuznach, Germany boast radium-rich springs which emit radon, as does Radium Springs, New Mexico.

Radon exhausts naturally from the ground, particularly in certain regions, especially but not only regions with granitic soils. Not all granitic regions are prone to high emissions of radon, for instance while the rock which Aberdeen is on is very radium rich the rock lacks the cracks required for the radon to migrate. In other nearby areas of Scotland (to the north of Aberdeen) and in Cornwall/Devon the radon is very much able to leave the rock.

Radon is a decay product of radium which in turn is a decay product of uranium. Maps of average radon levels in houses are available, to assist in planning mitigation measures.

While high uranium in the soil/rock under a house does not always lead to a high radon level in air, a positive correlation between the uranium content of the soil and the radon level in air can be seen.

In air

Radon harms indoor air quality in many homes. (See "Radon in Houses" below.)

Radon (²²²Rn) released into the air decays to ²¹⁰Pb and other radioisotopes and the levels of ²¹⁰Pb can be measured. It is important to note that the rate of deposition of this radioisotope is very dependent on the season. Here is a graph of the deposition rate observed in Japan.

Lead-210 deposition rate as a function of time as observed in Japan

In groundwater

Well water can be very rich in radon; the use of this water inside a house is another route allowing radon to enter the house. The radon can enter the air and then be a source of exposure to the humans, or the water can be consumed by humans which is a different exposure route.

Radon in rainwater

Rainwater can be highly radioactive due to high levels of radon and its decay progenies ²¹⁴Bi and ²¹⁴Pb; the concentrations of these radioisotopes can be high enough to seriously disrupt radiation monitoring at nuclear power plants. The highest levels of radon in rainwater occurs during thunderstorms, and it is hypothesized that radon is concentrated in thunderstorms on account of the atom's positive electrical charge. Estimates of the age of rain drops have been obtained from measuring the isotopic abundance of radon's short-lived decay progeny in rainwater.

In the oil and gas industries

Water, oil and gas from a well often contain radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point to propane.

In mines

Because uranium minerals emit radon gas, and their harmful and highly radioactive decay products, uranium mining is considerably more dangerous than other (already dangerous) hard rock mining, requiring adequate ventilation systems if the mines are not open pit. In the 1950s, a significant number of American uranium miners were Navajo, as many uranium deposits were discovered on Navajo reservations. A statistically significant subset of these miners later developed small-cell lung cancer, a type of cancer usually not associated with smoking, after exposure to uranium ore and radon-222, a natural decay product of uranium. The radon, which is produced by the uranium, and not the uranium itself has been shown to be the cancer causing agent. Some survivors and their descendants received compensation under the Radiation Exposure Compensation Act in 1990.

Currently the level of radon in the air of mines is normally controlled by law. In a working mine, the radon level can be controlled by ventilation, sealing off old workings and controlling the water in the mine. The level in a mine can go up when a mine is abandoned, it can reach a level which is able to cause the skin to become red (a mild radiation burn). The radon levels in some of the mines can reach 400 to 700 kBq m⁻³.

A common unit of exposure of lung tissue to alpha emitters is the working level month (WLM), this is where the human lungs have been exposed for 170 hours (a typical month worth of work for a miner) to air which has 3.7 kBq of ²²²Rn (in equilibrium with its decay products). This is air which has the alpha dose rate of 1 working level (WL). It is estimated that the average person (general public) is subject to 0.2 WLM per year, which works out at about 15 to 20 WLM in a lifetime. According to the NRC 1 WLM is a 5 to 10 mSv lung dose (0.5 to 1.0 rem), while the Organisation for Economic Co-operation and Development (OECD) consider that 1 WLM is equal to a lung dose of 5.5 mSv, the International Commission on Radiological Protection (ICRP) consider 1 WLM to be a 5 mSv lung dose for professional workers (and 4 mSv lung dose for the general public). Lastly the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) consider that the exposure of the lungs to 1 Bq of ²²²Rn (in equilibrium with its decay products) for one year will cause a dose of 61 μSv.

In humans a relationship between lung cancer and radon has been shown to exist (beyond all reasonable doubt) for exposures of 100 WLM and above. By using the data from several studies it has been possible to show that an increased risk can be caused by a dose as low as 15 to 20 WLM. Sadly these studies have been difficult as the random errors in the data are very large. It is likely that the miners are also subject to other effects which can harm their lungs while at work (for example dust and diesel fumes).

In houses

The fact that radon is present in indoor air has been known since at least the 1950s and research into its effects on human health started in the early 1970s. The danger of radon exposure in dwellings received more widespread public awareness after 1984, as a result of a case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Mr. Watras set off the radiation alarms (see Geiger counter) on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon in his basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day.

Depending how houses are built and ventilated, radon may accumulate in basements and dwellings. The European Union recommends that mitigation should be taken starting from concentrations of 400 Bq/m³ for old houses, and 200 Bq/m³ for new ones.

The National Council on Radiation Protection and Measurements (NCRP) recommends action for any house with a concentration higher than 8 pCi/L (300 Bq/m³).

The United States Environmental Protection Agency recommends action for any house with a concentration higher than 148 Bq/m³ (given as 4 pCi/L). Nearly one in 15 homes in the U.S. has a high level of indoor radon according to their statistics. The U.S. Surgeon General and EPA recommend all homes be tested for radon. Since 1985, millions of homes have been tested for radon in the U.S.

By adding a crawl space under the ground floor, which is subject to forced ventilation the radon level in the house can be lowered.