d) Sulfur. Sulfur in coal occurs in three forms: pyritic sulfur,
sulfate sulfur, and organic sulfur. The combustion of sulfur adds slightly to
the heating value of coal, but forms sulfur oxides (SOx) which are a closely
regulated pollutant. Sulfur oxides also combine with water to form an acid if
the combustion gas is cooled below its dew-point temperature. ASTM method
D 2492, Test Method for Forms of Sulfur in Coal, is a standard test which
determines the commonly recognized forms of sulfur in coal. Total sulfur is
determined by ASTM method D 3177, Test Method for Total Sulfur in the Analysis
Sample of Coal and Coke.
Fuel Oil. The term "fuel oil" denotes a large range of petroleum
products. Fuel oils are graded according to specific gravity and viscosity,
with the lightest being No. 1 and the heaviest being No. 6. Refer to Table 8.
Specific Gravity. The specific gravity of an oil is the ratio of
its weight to the weight of an equal volume of water. It is commonly
designated as "sp. gr. 60/60 F," indicating that both the oil and water are
weighed and measured at a temperature of 60 degrees F (15.5 degrees C). The
oil industry uses the API gravity scale, devised jointly by API and the
National Institute of Standards and Technology (NIST). The relationship
between specific gravity and API gravity is shown by the formula:
Deg. API Gravity =
Specific Gravity @ 60 NF
Since the specific gravity appears in the denominator of the equation, the
heavier the oil, the lower the API gravity.
Heating Value. The heating value per pound of fuel oil increases
with an increase in API gravity but heating value per gallon of fuel oil
varies inversely with API gravity because lighter oil contains more hydrogen.
Refer to Table 8.
Viscosity. The viscosity of an oil is the measure of its
resistance to flow. The viscosity of distillate oils is low enough not to be
critical. The heavier oils (grades 5 and 6) generally require heating for
satisfactory pumping and burning. Oil temperatures for efficient combustion
are determined by individual burner manufacturers. For typical pumping
temperatures, refer to Table 9.
Sulfur. As a rule, the percentage of sulfur in oil increases with
the grade number. The amount of sulfur can range considerably within each
grade due to variations in crude oils, refining processes, and blending.
Refer to Table 8. The combustion of sulfur in oil will lead to the same
pollution and corrosion problems as sulfur in coal.