Residual oil combustion

Three source classes were selected for comparison of CMB and model results. Two were of an area source nature (road dust and automotive exhaust) and one point source category (residual oil combustion). These sources were selected for comparison for the following reasons ... 

Residual oil combustion impact served as a test of the model s ability to predict point source emissions. Since vanadium and nickel emissions in Portland are almost totally associated with residual oil use, the CMB method was able to assign impacts with a high degree of confidence by using these two elements as chemical tracers. 

Another source of metallic contamination in the studied region comes from the residual oil combustion used for electric utilities and fluvial and terrestrial transportation. Using the selected emission factors (quantity of trace element released by quantity of material consumed) given by Nriagu and Pacyna (1988) and Nriagu (1989), the electric-power production installed in the Amazonian states and the fuel consumption used for transportation (Ministerio de Minas... 

Residual oil combustion can easily account for the observed vanadium concentration in the Boston atmosphere. We have not considered some other sources of particulates in the Boston area, notably refuse... 

The first commercial oil-fumace process was put into operation in 1943 by the Phillips Petroleum Co. in Borger, Texas. The oil-fumace blacks rapidly displaced all other types used for the reinforcement of mbber and today account for practically all carbon black production. In the oil-fumace process heavy aromatic residual oils are atomized into a primary combustion flame where the excess oxygen in the primary zone bums a portion of the residual oil to maintain flame temperatures, and the remaining oil is thermally decomposed into carbon and hydrogen. Yields in this process are in the range of 35 to 50% based on the total carbon input. A broad range of product quaHties can be produced. 

Atmospheric particulate emissions can be reduced by choosing cleaner fuels. Natural gas used as fuel emits negligible amounts of particulate matter. Oil-based processes also emit significantly fewer particulates than coal-fired combustion processes. Low-ash fossil fuels contain less noncombustible, ash-forming mineral matter and thus generate lower levels of particulate emissions. Lighter distillate oil-based combustion results in lower levels of particulate emissions than heavier residual oils. However, the choice of fuel is usually influenced by economic as well as environmental considerations. 

Reactions of contaminants in the fuel or air in the combustion zone can result in the formation of compounds which can condense as molten salts onto cooler components in the system. This type of process can occur when fuels containing sulphur or vanadium are burnt. In the case of sulphur contaminants, alkali sulphates form by reactions with sodium which may also be present in the fuel or in the combustion air, and for vanadium-containing fuels low-melting-point sodium vanadates or vanadium pentoxide are produced, particularly when burning residual oils high in vanadium. Attack by molten salts has many features in common which will be illustrated for the alkali-sulphate-induced attack, but which will be subsequently shown to be relevant to the case of vanadate attack. 

Carbon blacks are manufactured from hydrocarbon feedstocks by partial combustion or thermal decomposition in the gas phase at high temperatures. World production is today dominated by a continuous furnace black process, which involves the treatment of viscous residual oil hydrocarbons that contain a high proportion of aromatics with a restricted amount of air at temperatures of 1400-1600 °C. 

The use of EF values allows us to set limits on possible sources of elements. In Figure 1, EF values for six cities are compared with the ranges for particles from nine coal-fired power plants. For llthophlle elements such as SI, Tl, Th, K, Mg, Fe and many others not shown, E values are close to unity as expected, as these elements have mainly crustal sources, l.e., entrained soil and the aluminosilicate portion of emissions from coal combustion (see Table I). Many other elements are strongly enriched In some or all cities, and, to account for them, we must find sources whose particles have large values for those elements. Some are fairly obvious from the above discussions Pb from motor vehicles, Na from sea salt In coastal cities, and V and, possibly, N1 from oil In cities where residual oil Is used In large amounts (Boston, Portland, Washington). 

Coal-fired power plants release very large amounts of particulate material. The question Is, however, what fractions of the various elements In ambient air can be accounted for by particles from coal-fired plants A major fraction of an element can be contributed by coal combustion only If (1) coal accounts for an appreciable fraction of the A1 In the local atmosphere and (2) the EF value of the element on particles from coal combustion Is as great as for ambient particles. Only for those elements In Figure 1 for which there Is considerable overlap between the ranges for cities and for coal-fired plants can coal possibly be a major contributor. Even If there Is overlap, coal Is not necessarily a major source, as condition 1 above may not be met. On this basis, coal combustion could be a major source of many llthophlles plus Cr, N1, As, Se and, In cities where little residual oil Is used (Charleston and St. Louis), V. The very high EF values for As and Se and low values for V and Nl In Charleston, where little oil and a great deal of coal are burned, lends credence to this Interpretation. 

In the gas black process (Fig. 55), the feed stock is partially vaporized. The residual oil is continuously withdrawn. The oil vapor is transported to the production apparatus by a combustible carrier gas (e.g., hydrogen, coke oven gas, or methane). Air may be added to the oil-gas mixture for the manufacture of very small particle size carbon black. Although this process is not as flexible as the furnace black process, various types of gas black can be made by varying the relative amounts of carrier gas, oil, and air. The carbon black properties are also dependent on the type of burners used. 

Fuels for jet and gas-turbine engines are today being used in increasing quantities, a trend which is virtually certain to continue at an accelerated pace. Use of these fuels— petroleum fractions ranging from heavy naphthas through kerosine to residual oils, depending on the application—has by no means been free of problems, but so far few of those directly concerned with combustion efficiencies or mechanisms have been amenable to solution by use of additives. 

Table IV gives the properties of the SRC-II fuel oil compared to a low-sulfur residual oil utilized in a recent combustion test. The SRC-II fuel oil is a distillate product with a nominal boiling range of 350-900°F, a viscosity of 40 Saybolt seconds at 100°F and a pour point below -20°F. Thus, it is readily pumpable at all temperatures normally encountered in transportation of the fuel oil. The fuel oil has a very low content of ash and sediment as well as a low Conradson carbon residue. These characteristics are favorable from the standpoint of particulate emissions during combustion. Tests of compatibility with typical petroleum fuel oils and on stability of the coal distillates over time have not revealed any unusual characteristics that would preclude utilization of these coal-derived fuels in conventional boiler applications.

Although the preceding emissions data are consistent and follow predictable trends, they are not conclusive since they apparently contradict the level of combustion ineflBciency deduced from exhaust temperature measurements. It is known that temperatures over 1090 K are required for complete distillation of residual oil. However, since the gas... 

An unfortunate consideration associated with bleaching is the generation and subsequent disposal of the spent cake. Not only does the residual oil in the cake represent a loss to the processor, but spent cake is prone to spontaneous combustion under certain conditions when exposed to air. For that reason, spent cake may be classified as a hazardous material, making its environmentally responsible disposal difficult. The traditional landfill option may be restricted, not only because of this classification but also because of the limited space available at many locations. Spent cake can be added to meal in some cases, but this practice is frowned upon, especially when processing multiple types of oil. While deoiling the cake does help reduce the risk of combustion (and work is underway to reuse some of this material), most emphasis will be focused on alternate uses for the spent clay. Some... 

It is clear from Figure 5 that the combination of natural low sulfur fuels and fine gas desulfurization technology will not control the quantity and size range of combustion capacity required to achieve national ambient air quality standards. Thus, a third category of control technology, fuel desulfurization, is also included in Figure 5. These processes for not only desulfurization but total pollutant cleanup of coal and residual oil are required to achieve ambient air quality standards. Their basic role is two fold ... 

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