Residual Marine Fuel Oil (RMG) , FO380cst, FO180cst , Intermediate Fuel Oil (IFO), Heavy Fuel Oil (HFO)

Residual Marine Fuel Oil is the general classification of heavy fuel oil and is considered as the most important byproduct after gas oils and gasoline is extracted. It is manufactured to increase the production of light and middle distillates. Diesel ships were the first vessels to use Residual Fuel Oil followed by motor ships and steam ships. It helps in calculating carbon aromaticity index that indicates the ignition delay of fuel oil. Moreover, many power plants also use residual oil to cut the cost of the imported oil.

Residual Fuel Oil is made up of distillation residue. Fuel oil is mainly used in the diesel engines of marine ships. It is obtained during the process of crude oil refining. It consists of all the fuels that have non-boiling fractions. Depending on the temperature of the distillation process, the fuel oils are categorized into different grades. The most common forms of fuel oils are the viscous liquids that require heating for combustion and storage. The composition highly depends on the configuration of the refinery where crude oils are being processed.

Fuel oil is a fraction obtained from petroleum distillation, either as a distillate or a residue. Fuel oil is classified in six classes, numbered 1 through 6, according to its boiling point, composition and purpose.
No.1 is similar to kerosene and is the fraction that boils off right after gasoline.
No.2 is the diesel fuel that trucks and cars run on, leading to the name "road diesel".
No.3 is a distillate fuel oil and is rarely used.
No.4 fuel oil is usually a blend of distillate and residual fuel oils, such as No.2 and 6; sometimes it is just a heavy distillate (~ diesel distillate or residual fuel oil).
No.5 is a mixture of 75-80% of No.6 and 25-20% of No.2.
No.6 is called residual fuel oil (RFO) or heavy fuel oil (HFO). It is the remainder of the crude oil after gasoline and distillate fuel oils were extracted through distillation. It fuels thermal power stations or robust engines.

Residual fuel's use in electrical generation has also decreased. In 1973, residual fuel oil produced 16.8% of the electricity in the US. 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, produces uniformly higher carbon dioxide emissions than natural gas. 

A general classification for the heavier oils, known as No. 5 and No. 6 fuel oils, that remain after the distillate fuel oils and lighter hydrocarbons are distilled away in refinery operations. It conforms to ASTM Specifications D 396 and D 975and Federal Specification VV-F-815C. No. 5, a residual fuel oil of medium viscosity, is also known as Navy Special and is defined in Military Specification MIL-F-859E, including Amendment 2 (NATO Symbol F-770). It is used in steam-powered vessels in government service and inshore powerplants. No. 6 fuel oil includes Bunker C fuel oil and is used for the production of electric power, space heating, vessel bunkering, and various industrial purposes.

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 20th century, or which 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. Most of these facilities have subsequently been closed and demolished, or have replaced their fuel supplies 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 (which were usually designed without adequate corrosion protection in mind), 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, since the internal condensation produced sulfuric acid.

Residual fuel oil is something that is not admired or wanted by many. However, did you know that the transport of many consumer goods is dependent on it? Residual fuel oil is used to power the majority of vessels and large ships.

World trade is reliant on these cargo ships that use residual fuel oil. Residual fuel oil is basically the leftover fuel when oil is being produced.

The majority of oil is of very high value. However, the bits at the bottom of the barrel that aren’t of great value, which are often called scraps are the residual oils. Other names for these fuels are number 5 fuel oil, number 6 fuel oil, bunker fuel or maritime fuel oil.

The main expense for a vessel is generally fuel. For example, a large vessel making a long journey can easily spend up to £1 million on fuel. Depending on its speed and size, a ship can use between 60,000 and 400,000 litres of fuel in one day. However, bunker oil is more economical as it is less expensive than other fuels, such as diesel. This is good news for ship owners because as we saw above they consume a huge amount of fuel. That’s why ships use residual fuel. A journey may not always result in a profit for a ship; therefore it is important that the ship owner calculates the price of the fuel before making the journey.

To improve flow properties and viscosity, number 5 fuel oil also known as Bunker B is frequently blended with lighter oils.

Marine fuel oil or Bunker C is the oil that is left in the barrel after all the valuable oil has been removed. Therefore, it can be said that it is the 100% true residual oil. It is also referred to as number 6 fuel oil.

PHYSICAL AND CHEMICAL PROPERTIES
PHYSICAL STATE: Liquid. (Thick, oily liquid.)
COLOR: Brown to Black Viscous Liquid
ODOR: Strong Petroleum Odor, Asphalt like
BOILING POINT: 175 to 650°C (350 to 1200°F)
SPECIFIC GRAVITY: 0.93 to 1.0 (Water = 1) (@ 60° F)
VISCOSITY: 90 to 700 mm2
/s @ 50°C (cSt @ 122°F)
VAPOR PRESSURE: Not Determined
VAPOR DENSITY: >1 (Air = 1)
VOLATILITY: Negligible
EVAPORATION RATE: Negligible
MATERIALS TO AVOID: Strong acids, alkalis, and strong oxidizers.

NO. 6 FUEL OIL is manufactured to meet Standard Specification for Fuel Oils (ASTM D396) by blending high viscosity atmospheric tower bottoms (CAS 64741-45-3) and vacuum tower bottoms (CAS 64741-56-6) with lower viscosity catalytic cracked clarified oil (CAS 64741-57-57) to meet the viscosity specifications desired. The specific refinery streams used and the volumes used are dependent on the economic consequences of market alternatives and the target viscosity specification. Heavy residual fuels are complex mixtures of relatively high molecular weight compounds. Since they are blended from fractions with boiling points ranging from 650° to 1,200° F, the typical molecular weight range of the compounds is 600 to 1,000. Compound types include asphaltenes, polar aromatics, naphthene-aromatics, saturated hydrocarbons and heteromolecules containing sulfur, oxygen, nitrogen and metals. Fuels blended with catalytic cracked clarified oil contain some high molecular weight olefins and mixed aromatic-olefins. These cracked stocks contain greater proportions of highly condensed aromatics and fewer mixed aromatic and nonaromatic cycloparaffinic compounds than straight run stocks. The other commonly used blending stocks have lower molecular weight ranges than straight run residuals and are themselves complex mixtures that are difficult to characterize in detail. Appreciable concentrations of polynuclear aromatic hydrocarbons could be present in heavy residual fuels as a result of the nature of the blending stocks used and the common practice of including both crude and cracked residuals in the manufacture of the fuels.

Diesel engines, in particular low speed low speed marine propulsion engines, are often using residual fuel oils. These fuels are distinguished by differences in viscosity, boiling range, combustion characteristics, chemical composition and many other properties. They consist for the major part of residues from crude oil processing. A residual fuel is a mixture of several refinery streams like short residues, long residues, gasoil, cracked residues etc. Blends of these components are made to a specifications like viscosity, density sulphur content and stability. A viscosity specification is related to pumpability of the fuel in the customers plant and atomisation in the engine. A density specification is to assure the effectiveness of separators that are used to remove (traces of) water and other impurities from the fuel. A specification on sulphur content keeps the SO, emissions within limits. The stability specification prevents the flocculation or asphaltenes in the fuel, thus preventing blockage of filter systems and problems with injection pumps and injectors.

Residual fuels are extremely complex mixtures which can roughly be divided into paraffinic and naphtenidaromatic (asphaltenic) types according to crude oil origin. They can be considered as a dispersion of asphaltenes in an oily medium (the continuous phase) which is known as the ‘maltenes’. The definition of the asphaltenes and the maltenes relates to the fact that when a fuel is diluted with low molecular weight paraffinic solvent such as heptane, a brown or black precipitate is produced. The toluene soluble part of the precipitate is defined as asphaltenes, the remainder being impurities like sand, rust etc. The heptane soluble part of the fuel oil is defined as the maltenes. Thus the asphaltenes together with the maltenes comprise the residual fuel; the proportion of each will depend on the nature of the fuel oil.

Keywords, Residual Marine Fuel Oil (RMG) , FO380cst, FO180cst , Intermediate Fuel Oil (IFO), Heavy Fuel Oil (HFO) 

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