gas oil

Six classes

Fuel oil is classified into six classes, according to its boiling temperature, composition and purpose. The boiling point, ranging from 175 to 600 °C, and carbon chain length, 20 to 70 atoms, of the fuel increases with number. Viscosity also increases with fuel oil number and the heaviest oil has to be heated to get it to flow. Price usually decreases as the fuel number increases. No. 1 fuel oil, No. 2 fuel oil and No. 4 fuel oil are referred to as distillate fuel oils, diesel fuel oils, light fuel oils, gasoil or just distillate. For example, No. 2 fuel oil, No. 2 distillate and No. 2 diesel fuel oil are almost the same thing. Diesel is different in that it also has a cetane number limit which describes the ignition quality of the fuel. Distillate fuel oils are distilled from crude oil. Gas oil refers to the process of distillation. The show oil is heated, becomes a gas and then condenses. It differentiates distillates from residual oil (RFO). No. 1 is similar to kerosene and is the fraction that boils off right after gasoline. No. 2 is the diesel that trucks and some cars run on, leading to the name "road diesel". It is the same thing as heating oil. No. 4 is a distillate fuel oil and is rarely produced at a refinery. No. 5 fuel oil and No. 6 fuel oil are called residual fuel oils(RFO) or heavy fuel oils. However, since No. 6 is far more common than No. 5, the terms heavy fuel oil and residual fuel oil are sometimes used as synonyms for No. 6. They are what remains of the crude oil after gasoline and the distillate fuel oils are extracted through distillation, but No. 5 fuel oil is about 75-80% No. 6 and the rest is No. 2. No. 6 may also contain a small amount of No. 2 to get it to meet specifications. No. 4 fuel oil is usually a blend of distillate and residual fuel oils, such as No. 2 and 6, however, sometimes it is just a heavy distillate. No. 4 may be classified as diesel, distillate or residual fuel oil. Residual fuel oils are sometimes called light when they have been mixed with distillate fuel oil, while distillate fuel oils are called heavy when they have been mixed with residual fuel oil. Heavy gas oil, for example, is a distillate that contains residual fuel oil.

Bunker fuel

Bunker fuel is technically any type of fuel oil used aboard ships. It gets its name from the containers on ships and in ports that it is stored in, called bunkers. Bunker A is No. 2 fuel oil, bunker B is No. 4 or No. 5 and bunker C is No. 6. Since No. 6 is the most common, "bunker fuel" is often used as a synonym for No. 6. No. 5 fuel oil is also called navy special fuel oil or just navy special, No. 6 or 5 may also be known as furnace fuel oil (FFO said ef-ef-oh), and its high viscosity (thickness) requires it to be heated, usually by a reticulated low pressure steam system, before it can be pumped from a bunker tank.

Uses

Diesel has many uses. It heats homes and businesses and fuels trucks, ships and some cars. A small amount of electricity is produced by diesel, but it is dirtier and more expensive than natural gas. It is often used as a backup fuel for peaking power plants in case the supply of natural gas is interrupted or as the main fuel for small electrical generators.

Residual fuel oil is less useful because it is so viscous that it has to be heated, which requires a special heating system, before use and it contains relatively high amounts of pollutants, particularly sulfur, which forms sulfur dioxide upon combustion. However, its undesirable properties make it very cheap. In fact, it is the cheapest liquid fuel available. Since it requires heating before use, residual fuel oil cannot be used in road vehicles, boats or small ships, as the heating equipment takes up valuable space and makes the vehicle heavier. Heating the oil is also a delicate procedure, which is inappropriate to do on small, fast moving vehicles. However, power plants and large ships are able to use residual fuel oil.

Residual fuel oil was used more frequently in the past. It powered boilers, railroad locomotives and steamships. Locomotives now use diesel, steamships are no longer in use, and most boilers now use heating oil or natural gas. However, some industrial boilers still use it and so do a few old buildings, mostly in New York City. Residual fuel's use in electricity generation has also decreased. In 1973, residual fuel oil produced 16.8% of the electricity in the United States. By 1983, it had fallen to 6.2%, and as of 2005, electricity production from all forms of petroleum, including diesel and residual fuel, is only 3% of total production. The decline is the result of price competition with natural gas and environmental restrictions on emissions. For power plants, the costs of heating the oil, extra pollution control and additional maintenance required after burning it often outweigh the low cost of the fuel. Burning fuel oil, particularly residual fuel oil, also produces much darker smoke than natural gas, which affects the perception of the plant by the community.

The chief drawback to residual fuel oil is its viscosity, particularly in the case of No. 6 oil, which requires special apparatus for storage, pumping, and burning. Though it is still usually lighter than water (with a specific gravity usually ranging from 0.95 to 1.03)it is much heavier and more viscous than No. 2 oil, kerosene, or gasoline. No. 6 oil must, in fact, be heated to 150 °F (65.56 °C)–250 °F (121.1 °C) before it can be easily pumped, and in cooler temperatures it can congeal into a tarry semisolid. The flash point of most blends of No. 6 oil is, incidentally, about 150 °F (65.56 °C). Attempting to pump high-viscosity oil at low temperatures was a frequent cause of damages to fuel lines, furnaces, and related equipment.

Most of the facilities which historically burned No. 6 or other residual oils were industrial plants and similar facilities constructed in the early or mid 1900s, or who had switched from coal to oil fuel during the same time period. In either case, residual oil was seen as a good prospect because it was cheap and readily available, even though it provided less energy per gallon than lighter fuels. Most of these facilities have subsequently been closed and demolished, or have replaced their fuel suppies with a simpler one such as gas or No. 2 oil. The high sulfur content of No. 6 oil-- up to 3% by weight in some extreme cases-- had a corrosive effect on many heating systems, shortening their lifespans and increasing the polluting effects. This was particularly the case in furnaces that were regularly shut down and allowed to go cold; the internal condensation produced sulfuric acid.

Environmental cleanups at such facilties are frequently complicated by the use of asbestos insulation on the fuel feed lines. No. 6 oil is very persistent, and does not degrade rapidly. Its viscosity and stickiness also make remediation of underground contamination very difficult, since it reduces the effectiveness of methods such as air-stripping.

When released into water, such as a river or ocean, residual oil tends to break up into patches or tarballs-- mixtures of oil and particulate matter such as silt and floating organic matter- rather than form a single slick. An average of about 5-10% of the material will evaporate within hours of the release, primarily the lighter hydrocarbon fractions. The remainder will then often sink to the bottom of the water column.

Maritime

In the maritime field another type of classification is used for fuel oils:

• MGO (Marine gasoil) - roughly equivalent to No. 2 fuel oil, made from distillate only
• MDO (Marine diesel oil) - A blend of gasoil and heavy fuel oil
• IFO (Intermediate fuel oil) A blend of gasoil and heavy fuel oil, with less gasoil than marine diesel oil
• MFO (Medium fuel oil) - A blend of gasoil and heavy fuel oil, with less gasoil than intermediate fuel oil
• HFO (Heavy fuel oil) - Pure or nearly pure residual oil, roughly equivalent to No. 6 fuel oil

Marine diesel oil contains some heavy fuel oil, unlike regular diesels. Also, marine fuel oils sometimes contain waste products such as used motor oil.

Transportation

Fuel oil is transported by using barges and pipelines. The major physical supply chains of Europe are centered around the Rhine, Germany.

See also

• Diesel
• Gasoline
• Heating oil
• Jet fuel
• Kerosene
• Lubricant
• Naphtha

Sources

• National Park Service - Fuel Oil
• How Stuff Works - Oil Refining
• The True Cost of #6 Oil
• Burning #6 Fuel Oil
• Identity and Analysis of Total Petroleum Hydrocarbons
• Poten & Partners: Advisors to the Fuel Oil Industry