Of residual fuel

Noncatalytic partial oxidation of residual fuel oil accounts for the remainder of world methanol production. Shell and Texaco ate the predominant hcensors for partial oxidation technology (16) the two differ principally in the mechanical details of mixing the feedstock and oxidant, in waste heat recovery, and in soHds management. 

Visbreaking. Viscosity breaking (reduction) is a mild cracking operation used to reduce the viscosity of residual fuel oils and residua (8). The process, evolved from the older and now obsolete thermal cracking processes, is classed as mild because the thermal reactions are not allowed to proceed to completion. 

Contaminants in fuels, especially alkali-metal ions, vanadium, and sulfur compounds, tend to react in the combustion zone to form molten fluxes which dissolve the protective oxide film on stainless steels, allowing oxidation to proceed at a rapid rate. This problem is becoming more common as the high cost and short supply of natural gas and distillate fuel oils force increased usage of residual fuel oils and coal. 

In general terms, the life of a combustor might be reduced by about 30 percent through use of a distillate fuel and by 80 percent through the use of residual fuel. The first stage turbine nozzle life can Be reduced by 20 percent through use of a distillate fuel and by about 6.5 percent when certain residual fuels are used. 

Finally, the weight of a fuel, light or heavy, refers to volatility. The most volatile fuels vaporize easily and eome out early in the distillation proeess. Heavy distillates will eome out later in the proeess. What remains after distillation is referred to as residual. The ash eontent of residual fuels is high. 

See also Diesel Fuel Fossil Fuels Gasoline and Additives Kerosene Liquified Petroleum Gas Oil and Gas, Drilling for Oil and Gas, Exploration for Refining, Flistory of Residual Fuels. 

The residuum from vacuum distillation became, and still is, the basic component of residual fuel oil. It contains the heaviest fraction of the crude, including all the ash and asphaltenes. It is extremely high in viscosity and must be diluted with light distillate flux (a low viscosity distillate or residual fraction which is blended with a high viscosity residual fraction to yield a fuel in the desired viscosity range) to reach residual fuel viscosity. The lowest value distillates, usually cracked stocks, are used as flux. In some cases the vacuum residuum is visbroken to reduce its viscosity so that it requires less distillate flux. 

By the end ofWorld War II the use of residual fuel oil in the United States had reached about 1.2 million barrels per day. The bulk of this use was in industri-al/commercial boilers, railroad locomotives, and steamships. Shortly thereafter, railroad use declined rapidly as diesel engines, which used distillate fuel, replaced steam locomotives. In the 19.30s and 1960s residual fuel oil use for marine and industrial applications, as well as for electric power generation, con-... 

By 1973 about 1.4 million barrels per day of residual fuel oil were used for electric power generation in the United States. This accounted for 16.8 percent of U.S. electricity generation, mostly in areas where cheap, foreign heavy fuel could be delivered by tanker. That same year, another 1.4 million barrels per day of heavy fuel oil were used in the United States for industrial and commercial applications. Worldwide during 1973 about 2.6 million barrels per day of residual fuel oil were used in marine diesel engines, and another 1.1 million barrels per day were used for steamship propulsion. 

Wliile some refiners have reduced residual fuel production by supplying heavier grades, others have eliminated residtial fuel completely by installing cokers or hydrocrackers. These are process tmits that convert residua to gasoline or distillate. They are very expensive to install and operate, but can be justified when there is an oversnpply of residual fuel. 

The constituents of residual fuels are more complex than those of gas oils. A major part of the polynuclear aromatic compounds, asphaltenes, and heavy metals found in crude oils is concentrated in the residue. 

The main use of residual fuel oil is for power generation. It is burned in direct-fired furnaces and as a process fuel in many petroleum and chemical companies. Due to the low market value of fuel oil, it is used as a feedstock to catalytic and thermal cracking units. 

In the case of residual fuel firing for gas turbines it is necessary to provide extensive fuel-preparation plant for... 

Hennig [40] has applied ultraviolet spectroscopy to the determination of aromatic constituents of residual fuel oil in hexane extracts of marine sediment samples. Examination of the ultraviolet spectra of samples of an oil pollutant from a beach and crude oil, at various concentrations, revealed strong absorption maxima at approximately 228nm and 256nm. The ratio of the peak heights at these wavelengths is constant for a particular oil, and is independent of concentration. These permit quantitative analysis of sediment samples many months after an oil spill. 

Sediment usually consists of finely divided solids that may be dispersed in the oil or carried in water droplets. The solids may be drilling mud or sand or scale picked up during the transport of the oil, or may consist of chlorides derived from evaporation of brine droplets in the oil. In any event, the sediment can lead to serious plugging of the equipment, corrosion due to chloride decomposition, and a lowering of residual fuel quality. 

The significance of the measured properties of residual fuel oil is dependent to a large extent on the ultimate uses of the fuel oil. Such uses include steam generation for various processes, as well as electrical power generation and propulsion. Corrosion, ash deposition, atmospheric pollution, and product contamination are side effects of the use of residual fuel oil, and in particular cases, properties such as vanadium, sodium, and sulfur contents may be significant. 

Elemental analysis of fuel oil often plays a more major role that it may appear to do in lower-boiling products. Aromaticity (through the atomic hydrogen/carbon ratio), sulfur content, nitrogen content, oxygen content, and metals content are all important features that can influence the use of residual fuel oil. 

Viscosity is an important property of residual fuel oils, as it provides information on the ease (or otherwise) with which a fuel can be transferred from storage tank to burner system under prevailing temperature and pressure conditions. Viscosity data also indicate the degree to which a fuel oil needs to be preheated to obtain the correct atomizing temperature for efficient combustion. Most residual fuel oils function best when the burner input viscosity lies within a certain specified range. 

Production of kerosene has steadily decreased since 1970 (API 1991). The supply of kerosene produced in 1970 was 95,600,000 barrels. By 1975, production volume had dropped to 55,500,000 barrels. As of 1990, only 16,400,000 barrels of kerosene were produced. Production volumes of residual fuel oils showed a sharp increase between 1970 and 1980 and a sharp decline between 1980 and 1985 (lARC 1989). The total production volume of residual fuels in 1970 was 262,000,000 barrels, which increased to... 

Imports of residual fuel oils such as fuel oil no. 4 generally decreased in the period between 1975 and... 

API 1991). In 1975, total imports of residual fuel oil were 447,000,000 barrels however, imports gradually decreased over this 15-year period to 230,000,000 barrels in 1985. No information was located regarding diesel fuel imports or unspecified fuel oil imports. 

Reduction of residual fuel oil viscosity and sulfur content to meet specifications. 

It is impractical to determine the cetane number of residual fuels in the ASTM D-613 cetane engine. Because of this, the Calculated Carbon Aromaticity Index and the Calculated Ignition Index were respectively developed by Shell and BR These values can be determined from the following equations where d = Density in kg/m3 59°F (15°C) and v = Viscosity in cSt 122°F (50°C). 

This is one of the more important properties of residual fuel oil. It is an indication of both the pumpability characteristics of the fuel and the fuel atomization quality. 

The viscosity of residual fuel decreases rapidly with increasing temperature. If preheating is available, residual fuels atomize well. If preheating is not available, it may be necessary to bum lower-viscosity fuels rather than high-viscosity residual oils. 

The pour point of residual fuel is not the best measure of the low-temperature handling properties of the fuel. Viscosity measurements are considered more reliable. Nevertheless, residual fuels are classed as high pour and low pour fuels. Low-pour-point fuels have a maximum pour point of 60°F (15.5°C). There is no maximum pour point specified for high-pour-point residual fuels. A residual oil paraffin carbon number analysis is provided in FIGURE 3-1. 

Alumina, iron, nickel, silica, sodium, and vanadium are examples of compounds which can be found in residual fuel ash. If the vanadium content of residual fuel is high, severe corrosion of turbine blades can occur and exhaust system deposit formation can be enhanced. Vanadium-enhanced corrosion can occur at temperatures above 1200°F (648.9°C). 

Burning of sulfur to produce SO can create both burner system corrosion problems as well as atmospheric air emission concerns. About 1% to 5% of the fuel sulfur burned is converted to S03 and the remainder is converted to S02. If a system operates below its dew point, the SO, can react with condensed water to form sulfuric acid. Much work is being done through hydrodesulfurization, neutralization, and engineering to reduce the amount of sulfur oxides produced through burning of residual fuel. 

The pour point test is used to determine the lowest temperature at which a fuel can be effectively pumped. However, the pour point value can be misleading, especially when it is used to determine the low-temperature handling characteristics of residual fuel oil and other heavy fuels. Low-temperature viscosity measurements are considered more reliable than pour point values for determining the flow properties and pumpability of these oils. 

This method describes a procedure for determining the critical pour point of residual fuel oils. 

FIGURE. 7-1 Measurement of HS in the Vapor Phase of Residual Fuel Oil... 

PROBLEM INCREASE IN POUR POINT OF RESIDUAL FUEL OIL OR CRUDE OIL AFTER HEATING OR SHEARING... 

Griffith, M. G., and C. W. Sigmund. 1985. Controlling compatibility of residual fuel oils. In Marine Fuels, ed. Cletus H. Jones, pp. 227-247, Philadelphia American Society for Testing and Materials. 

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