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Fuel Oil

Fuel oils are comprised of mixtures of petroleum distillate hydrocarbons. The various kinds of fuel oils are obtained by distilling crude oil, and removing the different fractions. Fuel oil is any liquid petroleum product that is burned in a furnace for the generation of heat or used in an engine for the generation of power, except oils having a flash point of approximately 100 degrees F and oils burned in cotton or wool-wick burners. The oil may be a distillated fraction of a crude petroleum, a residuum from refinery operations, or a blend of these.

Two major categories of fuel oil are burned by combustion sources: distillate oils and residual oils. These oils are further distinguished by grade numbers, with Nos. 1 and 2 being distillate oils; Nos. 5 and 6 being residual oils; and No. 4 either distillate oil or a mixture of distillate and residual oils. No. 6 fuel oil is sometimes referred to as Bunker C. Diesel oils are among the products considered "fuel oils" in a broad sense.

The Department of the Navy uses a variety of petroleum fuels in support of naval operations, including gasoline, diesel, aviation gas, F-76, and navy special fuel oil (NSFO). There are many fuels commercially available both throughout the country and around the world. Fuels can have widely varying characteristics - but not all are suitable for use on Coast Guard vessels. Knowing the type of fuel you've taken onboard is also essential to good fuel management. Synonyms can be very confusing. Unfortunately, locally used fuel names often have no real meaning and may even be incorrect. For instance, "F-76" is sometimes mistakenly used to represent any commercial distillate marine fuel.

Heating Oil includes petroleum that is No. 1, No. 2, No. 4--light, No. 4--heavy, No. 5--light, No. 5--heavy, and No. 6 technical grades of fuel oil; other residual fuel oils (including Navy Special Fuel Oil and Bunker C); and other fuels when used as substitutes for one of these fuel oils. Heating oil is typically used in the operation of heating equipment, boilers, or furnaces. Heating fuel oil and transportation fuel oil no. 2 are basically compositionally the same.

By one syste, there are 3 grades of fuel oil. Light Fuel oil or Bunker A is used as fuel for small and general boilers. Medium Fuel Oil or Bunker B is used as fuel for medium boilers as well as and furnaces and stoves. Heavy Fuel Oil or Bunker C is often used as fuel for large furnace in industry e.g. a furnace for a cement processing plant.

Residual Fuel Oil is a topped crude oil or viscous residuum that, as obtained in refining or after blending with other fuel oil, meets or is the equivalent of Military Specification Mil-F-859 for Navy Special Fuel Oil and any more viscous fuel oil, such as No. 5 [Bunker B] or No. 5 [Bunker C]. When steamships were coal-fired,"bunkers" was the home for the bins used to hold the coal. As marine diesel engines became prevalent, the term was carried over to include the liquid fuel tanks. The United States Navy refers to Bunker C as "Navy Heavy". At one time, the lighter fuel oils Bunker A and Bunker B were also available. Bunker A oil is Bunker C cut with 20 percent diesel fuel. Fuel oil numbers 4, 5, and 6 are commonly known as "residual oils" since they are manufactured in whole or in part from distillation residues from refinery processing. These three heavy fuel oils are also known as gas oils and are composed of hydrocarbons ranging from C19 to C25. Residual oils are complex mixtures of relatively high molecular weight compounds and are difficult to characterize in detail. Molecular types include asphaltenes, polar aromatics, naphthalene aromatics, aromatics, saturated hydrocarbons and heteromolecules containing sulfur, oxygen, nitrogen, and metals. The viscous residuum fuel oils, numbers 5 and 6, sometimes referred to as bunker B and bunker C fuels, respectively, usually must be preheated before being burned.

Fuel Oil no. 5 consists of straight-run and cracked distillates and residuals, and contains aliphatics and aromatics. ASTM specifications list two grades of No 5, one of which is lighter and under some climatic conditions may be handled and burned without preheating. No. 5 fuel oil has two general categories: light and heavy. Light no. 5: This residual oil of intermediate viscosity is used in burners capable of handling fuel more viscous than fuel oil no. 4 without preheating. In some cases, preheating may be necessary in some types of equipment and in colder climates for handling. Heavy no. 5: This residual fuel oil is more viscous than grade no. 5 (light), but is intended for similar use. Preheating to 170-220 F is recommended before handling or use.

Fuel Oil Number 5 is typically about 75-80% Fuel Oil no. 6. Dimethyl and trimethyl naphthalenes are important components of Fuel No. 6 (and also no. 5). Most blending stocks of residual fuel oils are likely to contain 5% or more of four- to six-ring condensed aromatic hydrocarbons. This is important since some of the heavier polycyclic aromatic hydrocarbons (PAHs) are carcinogenic. The debates on which PAHs, alkyl PAHs, and other aromatics found in this product to classify as carcinogens, and the details of exactly how to perform both ecological and human risk assessments on the complex mixtures of PAHs typically found at contaminated sites, are likely to continue. There are some clearly wrong ways to go about it, but defining clearly right ways is more difficult. PAHs usually occur in complex mixtures rather than alone. Perhaps the most unambiguous thing that can be said about complex PAH mixtures is that such mixtures are often carcinogenic and possibly phototoxic.

Regarding potential effects on humans, chronic effects of some of the constituents in fuel 5 (including PAHs such as naphthalenes) include changes in the liver and kidney. Fuel oil #5 would be expected to be a skin, eye and respiratory irritant and a CNS depressant from inhalation of large amounts of the vapor or mist. Prolonged or repeated contact with the skin may produce a defatting dermatitis with dryness and cracking.

Navy Special Fuel Oil (NSFO) is a ship fuel, the equivalent of No. 5 heavy fuel oil that is produced by blending No. 6 fuel oil and light petroleum distillates. NSFO has a specific gravity similar to water, is a light non-aqueous phase liquid (LNAPL), and requires heating to be pumpable. These heavy fuel oils are highly viscous and possess high specific gravities.

Specialty fuels such as NSFO are less common; however they have a variety of physical and chemical properties that make remediation of these fuels more difficult. Subsequently, the amount of available information about remediation of these fuels is limited due to the lack of spill sites involving this unique fuel. Therefore, innovative remediation methods and technologies are needed to clean up these sites to meet state regulatory criteria. The physical and chemical properties of NSFO determine how it moves within the subsurface, its recoverability, and its ability to partition into other phases (i.e., vapor and dissolved). Viscosity of NSFO is the primary physical characteristic, which relates to mobility. NSFO has a viscosity of 170 centistokes at ambient temperature, which is 250 times that of gasoline, at 0.68 centistokes. Therefore, when released in a medium such as the site soils, which have an estimated porosity of 35 percent, NSFO is relatively immobile.

Fuel oil #6 / Bunker C is a petroleum distillate fraction with a boiling point > 400 degrees F. Fuel oil No. 6 is the highest boiling fraction of the heavy distillates from petroleum.Bunker "C" fuel oil is a sticky, black liquid similar in appearance and smell to asphalt sealing compounds. At 10 C it has a consistency of liquid honey or corn syrup. At 0 C it barely flows. No. 6 oils represent approximately 5 to 8% of the original crude petroleum, but the exact yield depends on the source, refinery design and operations, and product requirements. Fuel oil No. 6 contains about 15% paraffins, 45% naphthenes, 25% aromatics, and 15% non-hydrocarbon compounds; the hydrocarbons contain 30 and greater carbon atoms [557]. It consists of straight-run and cracked distillates and residuals and contains aliphatics and aromatics. Appreciable concentrations of polycyclic aromatic hydrocarbons (PAHs) are present in residual fuels because of the common practice of using both uncracked and cracked residues in their manufacture.

F-76 is the MIL-SPEC distillate fuel normally used in shipboard diesels, gas turbines, and boilers. F-76 has very tight specification and storage/handling quality control requirements. It is the fuel normally obtained directly from naval facilities and oilers. It has a minimum flash point of 60C (140F). Older naval engineering terminology referred to F-76 as Diesel Fuel Marine (DFM). Current practice no longer uses "DFM" as a descriptive name for F-76. To avoid confusion, F-76 fuel should only be referred to as "F-76". F-76 is never dyed.

MIL-F-16884 Fuel, Naval Distillate (NATO F-76) is the specification for F-76. F-76 is a specific MIL-SPEC fuel product that, as part of its spec requirements, must pass a rigorous storage stability test. However, no commercial fuel products come with a similar storage stability "guarantee". All commercial fuel therefore must be periodically rotated onboard ship - so that it's consumed before any potential stability problem can occur. All F-76 is subject to the accelerated storage stability test requirement upon procurement and again during long-term storage in compliance with MIL-STD-3004 (Quality Surveillance for Fuels, Lubricants and Related Products). A fuel passing the accelerated storage stability test requirement will be considered acceptable for normal storage conditions for at least 24 months. A fuel failing this test indicates that the fuel may become unstable in a shorter period of time. This period may be a few weeks or several months and cannot be determined by the current test method. The concern with F-76 failing this predictive test is the potential for the formation of particulates. This translates into increased fuel filter and fuel nozzle or injector plugging. What does this mean to the field operator? Nothing catastrophic -- although possibly increased filter change-outs would be indicated. This test is a predictor of the future and is no way indicative of the current fuel quality. An unstable fuel, as identified by ASTM D 5304, must be issued and burned before particulates begin to form in order to prevent problems. If the fuel currently meets all other F-76 requirements, the fuel is considered suitable for immediate issue and consumption. It should not be kept in long-term storage either onboard ship or at a shore terminal.

F-44 (JP-5) is a MIL-SPEC kerosene type jet fuel with a minimum flash point of 60C (140F). It also has very strict specification and storage/handling quality control requirements. JP-5 is ideally suited to FT-4 gas turbine engines. JP-5 can have a lower energy content than diesel fuels such as F-76 and NPD MGO (a nominal 5% difference). Its consumption rate may therefore be slightly higher. Burning JP-5 may also make achieving full power shaft rpm more difficult. JP-5 also contains a fuel system icing inhibitor (FSII) which is required for aviation use. This additive tends to migrate readily into any free water and has some anti-microbial properties. This means rigorous stripping procedures are critical if the anti-microbial activity of the icing inhibitor is to be realized. JP-5 is never dyed.

JP-5 is given as an exact synonym for kerosene and Fuel Oil 1, but this is not 100% correct. It is more precise to say that Jet fuel 5 (JP-5) is one particular form of no. 1 fuel oil. JP-1 is kerosene, while JP-5 is a specially refined kerosene, a high flash point kerosene. Jet Fuel 1 (JP-1) is listed as an exact synonym for kerosene according to several sources. Jet Fuel 5 is "heavy kerosene".

JP-5 is procured to MIL-DTL-5624T; Turbine Fuel, Aviation, Grades JP-4, JP-5, and JP-8 ST. JP-5 is a very clean burning fuel with very strict quality requirements - especially with regard to water and particulate content. Because it's an aviation fuel, it includes a Fuel System Icing Inhibitor (FSII) additive. JP-5 is inherently stable; it does not form oxygenated sludge. Gas turbine maintenance (particularly when associated with combustor cans) is reduced when burning JP-5. The downsides are that JP-5 tends to be more expensive; its energy content is lower than F-76 type fuel; and it may have lower viscosity and/or lubricity characteristics. The lower energy content means higher fuel consumption rates. Lower viscosity and lubricity may cause wear-type problems in diesel engine injection pumps.

B-76 is a special commercial product available under DESC bunker contracts in only a few domestic locations. This fuel product has identical properties to MIL-SPEC F-76 with the exception that the fuel can be dyed red and F-76 storage stability requirements have been waived. This means the storage stability characteristics of B-76 are similar to that of NPD MGO. B-76 also has a 6 month use limit.

DF2 is a special commercial product available under DESC bunker contracts in some domestic locations. This fuel product is based on a purely commercial fuel specification (ASTM D 975 Grade No. 2-D) and is the least preferred of the approved DESC bunker fuel products. DF2 has fewer and less stringent requirements than either NPD MGO or B-76. It also has a minimum flash point of only 52C (125F). Special precautions are therefore required when burning this fuel. The minimum cetane number/index is only 40 and may not meet the combustion quality requirements of all Coast Guard diesel engines. DF2 has no storage stability requirements; this means the storage stability characteristics of DF2 are identical to that of NPD MGO and B-76. DF2, therefore, also has a 6 month use limit. DF2 can be dyed red. An open market "number 2 diesel" fuel shall be treated as an emergency substitute fuel.

Navy Purchase Description Marine Gas Oil (NPD MGO) is a type of marine gas oil (100% distillate with no residual fuel contamination) that can be purchased from commercial sources under contract with DESC. Marine gas oil is a very broad classification of fuels, pertaining to their distillation temperature, general properties, and minimum flash point of 60C (140F). F-76, at one end of the quality spectrum, could be considered a marine gas oil, but so could fuels containing significant percentages of residual fuel (such as commercial Marine Diesel Fuel). The Navy Purchase Description has fewer and less strenuous requirements than the F-76 specification, but it does invoke additional requirements over what could otherwise be acceptable under a purely commercial specification (such as ASTM D-975 Grade No. 2-D). Storage and handling quality control is consistent with standard commercial practices. It is possible that fuel can meet the NPD MGO specification requirements, but be marketed under several different names, including "MDF" and/or "Commercial No. 2". As long as the fuel is obtained through a DESC contract, and ordered under National Stock Number 9140-01-313-7776 (domestic purchase) or 9140-01-417-6843 (overseas), cutters/boats will be assured of receiving fuel that meets the NPD MGO requirements. There is a 6 month time limit placed on the use of NPD MGO, starting when the fuel is taken onboard, due to concerns with storage stability. NPD MGO can be, but not necessarily will be dyed. In domestic ports, only red dye can be used. In overseas ports, other colored dye may also be used.

Emergency Substitute Fuels

Emergency substitute fuels may be used in an emergency, after determining that the product is acceptable. These fuels, in order of preference, are ASTM D-975 Grade No. 2-D (if not obtained from a DESC bunkers contractor) or ASTM D-396 No. 2; ASTM D-2880 No 2-GT; and Commercial MGO (100% distillate), from a commercial supplier not under a DESC contract. These fuels may not be suitable for long term use in marine gas turbines and/or some diesel engines. They may contain additives which could degrade coalescer/separator performance. Because they were not originally intended for marine use, their specifications may allow flash points lower than 60C (140F). The mixing of emergency substitute fuels with F-76, F-44 (JP-5), or NPD MGO is not recommended. Consolidate storage tanks before taking on emergency substitute fuels. Any emergency fuel taken onboard must be used as soon as possible. Storage stability will be a concern for all emergency substitute fuels.

Automotive Gas Oil (AGO) is the terminology for a fuel thatis sometimes requested as an emergency fuel. Like MGO, AGO is a very broad generic term and can describe a very wide range of fuel properties. It is likely to have a flash point less than 60C (140F). When offered AGO, determine what specific specification the fuel complies with and then apply the above criteria to determine suitability.

Flash point

Flash point is a measure of a fuel's flammability. The flash point affects a fuel's ease of ignition, flame spread rate once ignited, and extinguishing difficulty. As ambient temperature in a space approaches a fuel's flash point, the presence of flammable vapors increases dramatically. Marine fuel, by definition (and by international law), must have a minimum flash point of 60C (140F).

Prudent shipboard safety practice is to take on fuels with a minimum flash point of 60C (140F). However, due to market conditions in some parts of the world, only non-marine diesel fuel may be available. For example, DESC bunker fuel product DF2 has a minimum flash point value of 52C (125F). This product is currently available in only a few domestic locations. Emergency substitute fuels may also have flash points less than 60C (140F). In addition, flash points may routinely be as low as 52C (125F) in Mexican ports (year round). Risk is obviously highest for vessels that must routinely load low flash point fuel, but even a single low flash point fueling warrants special precautions. This is especially true in warm/hot operating environments.

In the winter months it is common commercial practice in some areas of the country to cut or blend No. 2-type diesel fuels with kerosene or No. 1-type diesel fuels to improve cold weather handling properties. However, this can lower the fuel's minimum flash point below 60C (140F). This practice is authorized by DESC bunkers contracts only in Alaska and only from 15 October to 15 April (the winter blend minimum flash point is 52C (125F)). However, the practice is becoming more common in many northern states and Canadian provinces. Low flash point winter blends may therefore be a concern in any open market purchase in cold climates. Note that the practice is prohibited on MIL-SPEC F-76 and JP-5 products.

Risk is minimal for vessels that burn the low flash point "winter blend" fuel solely in cold climates. This is due to generally colder ambient air and water conditions. SOLAS guidance states that storage and engineering space temperatures should be kept at least 10C cooler than the flash point of the fuel. This translates to a maximum safe engineering space air temperature of 42C (108F). However, vessels that are deployed to a cold climates, take on low flash point winter blend fuel, and then transit to warm or tropical waters with that low flash point fuel, are at increased fire risk.

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Page last modified: 07-07-2011 12:56:58 ZULU