In residual fuel

Nitrogen occurs in residua, and therefore in residual fuel oil, and causes serious environmental problems as a result, especially when the levels exceed 0.5% by weight, as happens often in residua. In addition to the chemical character of the nitrogen, the amount of nitrogen in a feedstock determines the severity of the process, the hydrogen requirements, and to some extent, the sediment formation and deposition. 

Low-pour-point fuel for use in residual fuel oil burners... 

The flash point identifies the minimum temperature at which fuel vapors will ignite. In residual fuel applications, this is helpful in determining whether fuel may be contaminated with high-flash materials. 

Catalyst fines, metals, rust, sand, and other material can be contained in residual fuel. These compounds arise from the crude oil, processing catalysts, water contamination, transportation, and storage of the fuel. If the total ash content is >0.20 wt%, deposits can form in burner systems and corrosion in high-temperature burners can occur. 

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). 

Filter plugging and burner problems can be caused by the presence of water-insoluble sediment and waterborne solids in residual fuel. Specifications on water and sediment typically range from 1 to 2 vol%. 

A wax can be defined as a linear, branched, or cyclic hydrocarbon typically containing from 17 to 60 carbon atoms. Low-carbon-number waxes are found in middle distillate fuels and typically constitute a low percentage of the paraffins found in distillate fuel. Higher-carbon-number waxes can be found in residual fuels and lubricating oil. The percentage of wax in residual fuel oils can vary widely depending upon the refining processes utilized. 

Both oil-soluble and water-soluble chemical scavengers can be added to fuel to remove hydrogen sulfide from oil and from water that may be contained in the fuel. Method ASTM D-5705 has been developed to help identify the presence of hydrogen sulfide in residual fuel oil. 

Determine the level of catalyst fine contamination in residual fuel. 

A variety of miscellaneous elements can also occur in residual fuel oil fraction For example, chlorine is present as a chlorinated hydrocarbon and can be determined (ASTM D-808, ASTM D-1317,ASTM D-6160). A rapid test method suitable for analysis of samples by nontechnical personnel is also available (ASTM D-5384) that uses a commercial test kit where the oil sample is reacted with metallic sodium to convert organic halogens to halide, which is titrated with mercuric nitrate using diphenyl carbazone indicator. Iodides and bromides are reported as chloride. 

The problem of instability in residual fuel oil may manifest itself either as waxy sludge deposited at the bottom of an unheated storage tank or as fouling of preheaters on heating of the fuel to elevated temperatures. 

Problems of thermal stability and incompatibility in residual fuel oils are associated with those fuels used in oil-fired marine vessels, where the fuel is usually passed through a preheater before being fed to the burner system. In earlier days this preheating, with some fuels, could result in the deposition of asphaltic matter culminating, in the extreme case, in blockage of preheaters and pipelines and even complete combustion failure. 

Anomalous viscosity in residual fuel oils is best shown by plotting the kinematic viscosity determined at the normal test temperature and at two or three higher temperatures on viscosity-temperature charts (ASTM D-341). These charts are constructed so that, for a Newtonian fuel oil, the temperature-viscosity relationship is linear. Nonlinearity at the lower end of the applicable temperature range is normally considered evidence of non-Newtonian behavior. The charts are also useful for the estimation of the viscosity of a fuel oil blend from knowledge of the component viscosities and for calculation of the preheat temperature necessary to obtain the required viscosity for efficient atomization of the fuel oil in the burner. 

Contamination in residual fuel oil may be indicated by the presence of excessive amounts of water, emulsions, and inorganic material such as sand and rust. Appreciable amounts of sediment in a residual fuel oil can foul the handling facilities and give problems in burner mechanisms. Blockage of fuel hlters (ASTM D-2068, ASTM D-6426) due to the presence of fuel degradation products may also result. This aspect of fuel quality control may be dealt with by placing restrictions on the water (ASTM D-95, IP 74), sediment by extraction (ASTM D-473, IP 53), or water and sediment (ASTM D-96, IP 75) values obtained for the fuel. 

The process described employs two extraction steps and two solvents to produce a high yield of low metals oil which is then suitable for use as a gas turbine fuel. The patentee relates that about 50% of the vanadium is present in residual fuel oil as a vanadyl porphyrin and the invention makes use of the relative solubilities of hydrocarbons and vanadyl porphyrin. 

Water content varies from 0.5 to 1%. Water is introduced into residual fuels by poor storage. The standards allow water up to a maximum of 1% in residual fuels. However, the majority of fuel deliveries have water contents below 0.5%. The problems with high water levels in fuel can be complex and include sludging of fuel tanks, filter blockage, corrosion of fuel injection equipment, exhaust valve corrosion, etc. 

Organic vanadium in residual fuel oil is converted to particulate vanadium oxide. Part of the calcium carbonate in the ash fraction of coal is converted to calcium oxide and is emitted to the atmosphere through the stack... 

THE ROLE OF TRACE METALS IN Table 5. Interlaboratory Study of Ni PETROLEUM. 9 in Residual Fuel Oil ... 

Approximately 38% of the residual fuel oil produced annually is burned in power plants.The remainder is used for a variety of other industrial and private uses. In industrial facilities a substantial fraction of the metals found in residual fuel oil is collected in the bottom ash and in fly ash produced during its combustion. Some of the more volatile metals and metal oxides are lost to the environment as vapors together with some of the very fine particulates, which are difficult to collect. Again, however, no data presently available describe the ultimate fate of metals in residual fuel oils. 

The presence of vanadium in petroleum crudes is well documented. Much analytical data " have been compiled because the metal brings about unfavorable effects in poisoning cracking and other catalysts in the standard refinery operations. Furthermore, presence of vanadium in residual fuels at high levels results in damage to furnace components. 

The total amount of vanadium in residual fuel oil is probably greater than in any other product of petroleum refining. About 668 million barrels of fuel oil were consumed in the United States in 1968, and this material is estimated to have contained nearly 19,000 tons of vanadium. At the current price, this amount of vanadium is worth about 100 million. Desulfurization of fuel Oil can reduce the vanadium content about proportionate to the reduction of sulfur.If fuel oil is desulfurized to reduce atmospheric pollution, can a significant amount of vanadium be recovered profitably from the catalysts used in the desulfurizing process or at some other stage in this process ... 

Methods for burning mixtures of pulverized coal in oil (variously called colloidal fuel, coal-in-oil slurry, or coal-oil suspension) have been studied for nearly a century and require the production of coal-in-oil suspensions. Stable short-term suspensions of coal in residual fuel oil are easily attained if the coal is pulverized to 200 mesh (75 am) and, by adding surfactants, long-term stability can be obtained so that the coal will not settle out of the mixture even over periods as long as a few months. The interaction between the coal and the hydrocarbon allows the apparent viscosity of the coal-oil mixture (COM) to be 10 times greater than the fuel oil base and special precautions may be taken to provide adequate pump capacity, heating systems for the slurry, and properly sized burner nozzles. 

Duyck et al (2002) determined Ag, Al, Ba, Cd, Co, Cu, Fe, La, Mg, Mo and Mn in residual fuel oil and crude oils by ICP-MS after dilution of the samples in toluene, using ultrasonic nebulization. Good accuracy was reported for the determinations of the metals. Wondimu et al (2000) analysed residual fuel oil for Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe and Hg by ICP-MS after micro-wave acid decomposition. H2O2 was used after acid decomposition for better carbon removal. Lord (1991) determined Li, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Ag, Cd, Sn, Sb, Ba and Pb in crude oils by ICP-MS with mciro-emulsion sample introduction. Kowalewska et al (2005) determined Cu in crude oils and crude oil distillation products by ICP-MS after ashing and micro-wave assisted decomposition of analyte and transferred to aqueous solution. Good recovery of Cu was reported. Kelly et al (2003) determined Hg in crude oils and refined products by cold Vapor ICP-MS after decomposition of the sample by closed system combustion. Botto (2002) analysed crude oil, petroleum naphthas and tars for Na, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Mo, Cd, Sn, Sb,... 

---