Fuel Oils

In many large furnaces, fuel oils are used as the primary fuel. Fuel oils consist of the following constituents:

a. Carbon

b. Hydrogen

c. Oxygen

d. Sulfur

e. Nitrogen

f. Moisture (minor constituent)

g. Ash (minor constituent)

The term “ash” refers to the solid mineral constituents that are not combustible, and therefore do not contribute to the combustion process.

For common usage, fuel oils are categorized in five different classifications: From No. 1 to No. 6.

No. 1 is the lightest (low density and low viscosity) oil, while No. 6 oil has the highest density and viscosity.

No. 1 Oil: Distillate (kerosene). Light color.

No.2 Oil: Distillate. Amber color.

No. 4 Oil: Very light residual. Dark color.

No. 5 Oil: Light residual. Dark color.

No. 6 Oil: Residual. Also called bunker C oil. Dark color.