Fuel Oil

Fuel oil is a mix of hydrocarbons which is obtained by diluting a high viscosity residue with a distillate, called flux.
In the refineries without conversion plants the residue is that from atmospheric distillation, while in more complex refineries the residue can be of different types, for example, from vacuum distillation, according to the technical structure of the plant .
Stocks from primary distillation such as kerosene or diesel fuel from cracking plants can be used as fluxes.
The main use of fuel oil is in stationary combustion for the production of steam for industrial uses or for the generation of electric energy.
Another very important use is that on large diesel motors for the propulsion of ships or for the production of electric energy in small power plants.

The quality of fuel oil for stationary uses is regulated on a national level by DPCM (Prime Minister Decree) 8 March 2002, the fuel oil is classified based on the viscosity and on the sulphur content.

Based on the viscosity, the fuel oil can be defined as:

• Light, with viscosity between 3° and 5° Engler at 50 °C 
• Heavy, with viscosity > 12° Engler at 50 °C

Based on the sulphur content, the light fuel oil can be defined as:

• BTZ, with sulphur content < 1% in weight 
• STZ, with sulphur content < 0,3% in weight

 While heavy fuel oil can be defined as: 

• ATZ, with sulphur content < 3% in weight
• BTZ, with sulphur content < 1% in weight
• STZ, with sulphur content < 0,3% in weight

The quality of fuel oil for marine use is regulated on a global level by the ISO 8217 regulation. The various types of bunkers generally differ from a regulation point of view only for viscosity.
The European Union is considering the regulation of a bunker type with less sulphur content.