Page 112 - Synthetic Fuels Handbook

98 CHAPTER THREE

kerosene fractions may need only a lye wash or a doctor treatment if hydrogen sulfide is
present to remove mercaptans.
Kerosene has been used as a fuel oil since the beginning of the petroleum-refining indus-
try. As such, low proportions of aromatic and unsaturated hydrocarbons are desirable to
maintain the lowest possible level of smoke during burning. Although some aromatics may
occur within the boiling range assigned to kerosene, excessive amounts can be removed
by extraction; that kerosene is not usually prepared from cracked products almost certainly
excludes the presence of unsaturated hydrocarbons.
The essential properties of kerosene are flash point, fire point, distillation range, burning,
sulfur content, color, and cloud point. In the case of the flash point (ASTM D-56), the mini-
mum flash temperature is generally placed above the prevailing ambient temperature; the fire
point (ASTM D-92) determines the fire hazard associated with its handling and use.
The boiling range (ASTM D-86) is of less importance for kerosene than for gasoline,
but it can be taken as an indication of the viscosity of the product, for which there is no
requirement for kerosene. The ability of kerosene to burn steadily and cleanly over an
extended period (ASTM D-187) is an important property and gives some indication of the
purity or composition of the product.
The significance of the total sulfur content of a fuel oil varies greatly with the type of
oil and the use to which it is put. Sulfur content is of great importance when the oil to be
burned produces sulfur oxides that contaminate the surroundings. The color of kerosene is
of little significance, but a product darker than usual may have resulted from contamination
or aging, and in fact a color darker than specified (ASTM D-l56) may be considered by
some users as unsatisfactory. Finally, the cloud point of kerosene (ASTM D-2500) gives
an indication of the temperature at which the wick may become coated with wax particles,
thus lowering the burning qualities of the oil.

Fuel Oil. Fuel oil is classified in several ways but generally may be divided into two main
types: distillate fuel oil and residual fuel oil. Distillate fuel oil is vaporized and condensed
during a distillation process and thus have a definite boiling range and do not contain high-
boiling constituents. A fuel oil that contains any amount of the residue from crude distilla-
tion of thermal cracking is a residual fuel oil. The terms distillate fuel oil and residual fuel
oil are losing their significance, since fuel oil is now made for specific uses and may be
either distillates or residuals or mixtures of the two. The terms domestic fuel oil, diesel fuel
oil, and heavy fuel oil are more indicative of the uses of fuel oils.
Diesel fuel oil is also a distillate fuel oil that distils between 180 and 380°C (356 and
716°F). Several grades are available depending on uses: diesel oil for diesel compression
ignition (cars, trucks, and marine engines) and light heating oil for industrial and com-
mercial uses.
Heavy fuel oil comprises all residual fuel oils (including those obtained by blending).
Heavy fuel oil constituents range from distillable constituents to residual (nondistillable)
constituents that must be heated to 260°C (500°F) or more before they can be used. The
kinematic viscosity is above 10 cSt at 80°C (176°F). The flash point is always above 50°C
(122°F) and the density is always higher than 0.900. In general, heavy fuel oil usually
contains cracked residua, reduced crude, or cracking coil heavy product which is mixed
(cut back) to a specified viscosity with cracked gas oils and fractionator bottoms. For some
industrial purposes in which flames or flue gases contact the product (ceramics, glass, heat
treating, and open hearth furnaces) fuel oils must be blended to contain minimum sulfur
contents, and hence low-sulfur residues are preferable for these fuels.
No. 1 fuel oil is a petroleum distillate that is one of the most widely used of the fuel oil
types. It is used in atomizing burners that spray fuel into a combustion chamber where the
tiny droplets burn while in suspension. It is also used as a carrier for pesticides, as a weed
killer, as a mold release agent in the ceramic and pottery industry, and in the cleaning industry.